Follow along here for the biggest moves around Europe as they happen in the final hours of the summer transfer window.
Transfer deadline day has come and gone!
It's been a wild summer of transfers and rumors, with clubs spending into the billions around Europe to remake their rosters in hopes of securing titles, Champions League places and the continent's top crown.
Neymar's move from Barcelona to PSG has by far been the must stunning and costly transfer of the summer, but by no means is it the only one. He's got a new teammate at PSG after Kylian Mbappe's sensational loan move from Ligue 1 rival Monaco. Not all big names expecting to move on deadline day did, though. Alexis Sanchez's move to Manchester City never materialized, nor did Thomas Lemar's move to Arsenal. Riyad Mahrez hasn't moved from Leicester City, nor has Virgil Van Dijk from Southampton or Ross Barkley from Everton.
Plenty of players did move, though. Here are the ones around Europe–with a reminder that Spain's deadline does not hit until Friday.
Paris Saint-Germain have officially completed the signing of hugely coveted Monaco starlet Kylian Mbappe on an initial season-long loan, with an obligation to buy next summer in a permanent deal rumoured to be worth up to €180m.
The 2018 fee is set to make 18-year-old Mbappe the second most expensive player of all time behind only Brazilian superstar Neymar, who he will now be able to count among his team-mates in Paris - and is back in his home city.
The deal will see Mbappe sign a four-year contract to 2022 at the end of the loan.
The teenager took French and European football by storm after a breakout campaign in 2016/17. He scored 26 goals in all competitions, six of which came in the Champions League, as Monaco captured a first French title in 17 years and made it to the semi-finals in Europe.
"It is with great joy and pride that I join the Paris Saint-Germain," Mbappe told PSG.fr.
"For any young person from the Paris region, it is often a dream to wear the red and blue jersey and to taste the unique atmosphere of the Parc des Princes," he added.
"I was seduced by the project of the club, it is one of the most ambitious in Europe. Along with my new teammates, I intend to continue my progression today while helping the team to achieve the very big objectives it has set itself."
Mbappe had inherited Monaco's number 10 shirt for the 2017/18 season, moving down from number 29. But with his expected departure now sealed, that jersey has already been assigned to Stevan Jovetic, a new arrival in the principality from Inter Milan.
Liverpool have confirmed the signing of Alex Oxlade-Chamberlain from Arsenal for a reported fee of up to £40m on their club website.
Three-time FA Cup winner Oxlade-Chamberlain put pen to paper on a six-year deal with Liverpool ahead of the deadline day cut off and could now make his debut for his club after the international break, against Manchester City on September 9.
Arsenal had also accepted an offer of similar value from London rivals Chelsea, but the 24-year-old rejected the move in order to seal a transfer to Liverpool and completed his medical at St George's Park, while on duty with the England national team, on Wednesday evening.
Liverpool had been linked with a move for Oxlade-Chamberlain, who had just one year left on his Arsenal contract, for some time and reports suggest he turned down Chelsea in order to play for his boyhood club and compete for berth in his favoured central midfield position.
“Firstly, I’m delighted to have signed for Liverpool and a big thank-you to everyone here at the FA that has made this possible, using the facilities. It has been a massive help," Chamberlain told the club website.
“I’m here with England and we’ve got two big games coming up, so I want to focus on them. But I can’t wait to get to Melwood and you’ll hear first from me on LFCTV.”
The former Southampton starlet, who joined Arsenal for an initial £12m in 2011, became the Gunners' record departure with his fee, which is reported to be £35m with £5m add-ons.
While Liverpool could also yet make deadline day swoops for Monaco's Thomas Lemar and Southampton's Virgil van Dijk. However, BBC Sport journalist David Ornstein has suggested that Arsenal are 'unlikely' to sign a replacement.
Tottenham Hotspur have officially completed the signing of versatile Ivory Coast international defender Serge Aurier from Paris Saint-Germain in a deal believed to be worth £23m.
Aurier, who replaces Kyle Waker in the Spurs squad following his exit to Manchester City earlier this summer, has agreed a five-year deal with the north London club.
The biggest complication in the deal had been organising a work permit for Aurier, who received a suspended prison sentence after assaulting a police officer in Paris last year.
As a result, the player had been prevented from even entering the United Kingdom But he was eventually granted the paperwork and given Home Office clearance on Wednesday.
Aurier is the latest defensive acquisition for Spurs since last season after existing deals for South American duo Davinson Sanchez and Juan Foyth from Ajax and Estudiantes respectively.
Kevin Wimmer left the club for Stoke earlier this week as he seeks more playing time.
Having started his professional career with Lens after moving to France as a 13-year-old, Aurier rose to prominence during his time with Toulouse and joined PSG, initially on loan, in 2014.
He won domestic trebles in each of his first two seasons in the capital, adding further cup and league cup honours in 2016/17 as Monaco wrestled the Ligue 1 title away.
Swansea have officially completed the signing of Renato Sanches from Bayern Munich on a season-long loan deal, in what is arguably one of the most eyebrow-raising transfers of the summer.
The 20-year-old had been linked with the likes of Liverpool, Manchester City, Chelsea, Monaco, Juventus, AC Milan to name but a few, but Swansea have somehow managed to pull off the coup.
Sanches was hailed as one of the hottest young prospects in world football following his showing at Euro 2016 but his progression has halted since then.
He failed to kick on in the way people expected him to last season and wasn't even selected by Portugal for the recent Confederations Cup.
Bayern CEO Karl-Heinz Rummenigge had said this morning that the deal was set to go through, and now the club have provided official confirmation of the move via their official website and social media channels.
Sanches will be a direct replacement for the departed Gylfi Sigurdsson and will be bidding to remind his parent club just how much ability he has.
Had he remained at the Allianz, he would have had to fight for his place in centre midfield with Arturo Vidal, Thiago Alcantara, Corentin Tolisso, Sebastian Rudy and James Rodriguez.
Chelsea have completed a beyond-deadline day deal to sign 2015/16 title winner Danny Drinkwater from Leicester City, in a transfer believed to be worth over £30m.
Drinkwater arrived at Chelsea's Cobham training ground for a medical on Thursday evening, with an extension beyond the 11pm cut-off point granted to allow the paperwork to be finalised. The move was first announced by Leicester at 1:30am, before Chelsea soon confirmed the deal would keep him at Stamford Bridge for five years.
Drinkwater said: "I’m delighted to be a Chelsea player and can’t wait to get started. It has been a long journey to get here but I am very happy and am looking forward to helping the club win more trophies."
Technical director Michael Emenalo added: "Danny is not only a Premier League winner but also has Champions League experience which will be invaluable for us this season. He is a typically combative English midfielder with a cultured passing technique and his arrival significantly strengthens our midfield options."
Having started his career in the youth ranks at Manchester United, Drinkwater joined Leicester on a permanent deal in 2012 after a number of loan spells elsewhere. He was a key member of the Foxes team that topped the Championship to earn promotion in 2013/14 and was again a star performer two years later when the club pulled off the most unlikely of Premier League title wins.
Drinkwater was rewarded with is first senior England cap in March 2016 and will be looking to add to his three caps now that he has made the move to Chelsea.
Tottenham Hotspur have completed a deadline day deal for striker Fernando Llorente for a reported fee of £12m.
The 32-year-old striker had been expected by many to join Chelsea after the Swans accepted an offer earlier on Thursday, but Antonio Conte has been left frustrated as the player who played under him at Juventus has instead opted to move to Spurs on a two-year deal.
Spurs confirmed the deal on their club website and the forward, whose deal apparently includes the option for a one-year extension after the end of the 2018/2019 season.
The announcement comes as yet another bitter blow to Chelsea, who have also lost out in moves for Romelu Lukaku and Alex Oxlade-Chamberlain, who opted for the Blues rivals Manchester United and Liverpool respectively.
Basque-born Llorente, who has 27 caps for Spain and was part of the 2010 World Cup winning side, scored 15 times for Swansea in his first season in English football in 2016/17 and played an important role in keeping Paul Clement's side in the Premier League.
Llorente, whose move could signal the imminent departure of fellow striker Vincent Janssen, is Tottenham's second transfer deadline day signing following Serge Aurier's arrival on a five-year deal.
After completing a transfer deadline day move worth around £26m from Liverpool to Crystal Palace, Mamadou Sakho has revealed why returning to Selhurst Park was always his preferred destination this summer.
Sakho made eight appearances for Crystal Palace on loan in the latter half of the 2016/17 campaign, helping the Eagles to avoid relegation, and the French defender admitted he couldn't wait to return, having penned a four-year deal with the North London side.
In a statement on the Crystal Palace club website, the 27-year-old stated just how eager he was to return
He said: "I loved the challenge last year; it was difficult but beautiful and it’s why this summer I thought that Palace was the best choice,
"I am really happy to be here because I have some friends here. I still keep in touch with Christian, Wilf, Bakary and Yohan Cabaye, as well as Jason Puncheon. We had a really good ambiance last year and so we still speak to each other."
After his first stint with Crystal Palace was cut short by a serious knee injury, Sakho has been working himself back to full fitness over the summer at Liverpool's training camp, Melwood, and will be hoping to be fit enough to pull on the Palace jersey sooner rather than later.
Speaking on his injury, he said: "I feel really good and trained really hard to try to come back at 100% level. I am still having treatment and I’m starting to train again, so we’ll see with the doctor and the physio how far away I am to starting a full game."
Palace's acquisition of Sakho for the tail end of last season may have proven crucial to them beating relegation, and fans will be hoping he will have a similar, positive impact on the Eagles in the new campaign.
After spending the summer training with Liverpool, Sakho is eager to return to training with Palace and to work under new boss, Frank de Boer.
"I am really excited about playing for the Palace fans again, but in football the past is the past and you need to think about today and tomorrow,” he added. "Last year we did a good job and we need to prove that again and have a good objective. If we put all of our power together, we will have a great season.
"I think we also have a really good manager with a lot of experience. He has a new football mentality and we have a great squad so we just need to work hard, and I think that everything will be better soon.
"I fought for PSG for many years and was proud to do that, and I did that as well for Liverpool. Today is a new story for me; I will start to fight again for Palace and I’m proud at the same level. Whatever shirt I wear I give 100%, and I will try to give my best here."
Chelsea have completed the signing of Italian full-back Davide Zappacosta in a late deadline day deal to help strengthen the squad ahead of what promise to be a challenging few months for the reigning Premier League champions.
Chelsea missed out on deals for Alex Oxlade-Chamberlain, Ross Barkley and Fernando Llorente in the final 24 hours of the summer transfer window, but captured Zappacosta on a four-year contract in a transfer believed to be worth £23m.
"It is a dream for me to join Chelsea and play in the Premier League. I am very excited to be here and start working with the team. I hope I can show my quality to the coach, my team-mates and the supporters," the 25-year-old told his new club's official website.
Technical director Michael Emenalo commented, "Davide is a player of international calibre who Antonio Conte knows well and we have been aware of for some time. We are very pleased to be able to bring him to the club and believe he will become an important member of the squad."
Zappacosta joined Torino from Atalanta in 2015, having initially started his career in the Italian lower leagues with Isola Liri and Avellino.
Wilfried Bony has been reunited with Swansea City after he completed a transfer back from Manchester City for a fee believed to be in region of £12m.
The striker, who left south Wales to join the Premier League heavyweights in January 2015, has signed a 2-year contract, with the option of a third, after he completed a medical at the club's training ground on Thursday.
The announcement was made via Swansea's Twitter account, and brings to an end Bony's miserable spell at the Etihad since his £25m move up north two-and-a-half seasons ago.
Reacting to the confirmed switch, Swans boss Paul Clement explained why he had been keen to bring the Ivory Coast international back to the Liberty Stadium.
Bony was a one-in-two goal marksman at Swansea before he departed for City, with 35 goals plundered in just 70 appearances for the 2013 League Cup winners.
The 28-year-old was the Swans' talisman for 18 months before he was lured away with the riches on offer by the two-time Premier League champions, but his time in the north west of England wasn't all it was cracked up to be.
Bony found the net just 11 times in 46 appearances for City and, after being shipped out on loan to Stoke City last term, managed just two strikes in 10 games for Mark Hughes' Potters.
Serie A side Hellas Verona appeared set to entice Bony away from Manchester temporarily again as they eyed a season-long loan for him, but Swansea's intervention scuppered that move at the last moment.
The former Vitesse forward will replace the outgoing Fernando Llorente as the main competition for Chelsea loanee Tammy Abraham, with the Spain international on the cusp of completing a shock move to Tottenham Hotspur.
Everton have completed the £8m signing of talented Hajduk Split winger Nikola Vlasic.
The Croatia international has penned a [length]-year contract with the Toffees after the announcement was made on the club's official website on Thursday.
Vlasic, like Henry Onyekuru before him, will be immediately loan out by manager Ronald Koeman to [team here] to further his footballing development before potentially joining up with the first-team squad next season.
Croatia's Under-21 side allowed Vlasic to leave their training base on Wednesday to fly to England to complete his switch to Goodison Park and, after a successful medical, has become the ninth signing of a productive summer for Koeman's outfit.
Speaking about the capture of one of the most promising talents in Eastern Europe, Koeman stated why he decided to bring Vlasic to Merseyside.
He said: “I am very excited about the opportunity to play for this big club,” said the Croatia international. “The Premier League is the best league in the world and this is one of the top clubs in England. It is such a big honour for me to be here.
“When I heard that Everton were interested in me, I knew straight away I wanted to come here. Whenever someone called my manager or my father, I told them I only wanted to come to Everton."
Vlasic impressed Everton's senior staff when the Blues and Hajduk locked horns in the recent two legged Europa League play-off tie - a clash that Everton won 3-1 - as he showed off his silky footwork, work ethic and delivery from the flanks.
The teenager originally joined Hajduk as a 12-year-old from former outfit Omladinac Vranjic, and made his senior bow for the HNK.1 giants at 16 years of age in a Europa League match against Irish team Dundalk in July 2014.
Vlasic scored in that match and, in the process, became the club's youngest ever goalscorer in international competition. He was also made vice-captain of Hajduk last June at just 18-years-old, such was the esteem he was held in by the club's managerial team.
Vlaic's talent and potential had seen linked with big-money moves to the likes of Tottenham Hotspur, but it is Everton who have taken a punt on bringing him to the Premier League instead.
The 19-year-old, who can play anywhere across the forward line, has made appearances and bagged goal and assists during his stay at Stadion Poljud.
Inter Milan flop Gabriel Barbosa has left the club, according to their official site, to join Benfica on loan for the duration of the 2017/18 season, with the Portuguese champions holding an option to make the deal permanent.
Gabriel, often referred to as Gabigol, joined Inter from Santos in a deal worth close to €30m just last summer. He was billed as the next big thing to emerge from Brazil and was as hyped as much as fellow youngster Gabriel Jesus prior to his move from Palmeiras to Manchester City.
But where Jesus has flourished since arriving in Europe, Gabriel has floundered.
He failed to establish himself at Inter, playing only sparingly in all competitions throughout the 2016/17 campaign, and will hope to get his career back on track in Portugal.
The absence of a language barrier may well help the 20-year-old settle better in Lisbon.
Arsenal forward Joel Campbell has officially left the club on loan for the sixth time as he joins Real Betis for the duration of the 2017/18 season.
Campbell joined the Gunners from Saprissa in his native Costa Rica in 2011 but has only spent 18 months in the first-team during that time.
The loan move to Betis will mark his second spell at the Seville-based club after an earlier stint during the 2012/13 campaign. He had previously played with Lorient on loan in 2011/12, while there have been loans to Olympiacos, Villarreal and Sporting CP in the years since.
Campbell, now 25 years of age, was a star of the 2014 World Cup as Costa Rica defied the odds to top a tough group containing England, Italy and Uruguay and then come within a penalty shootout of reaching the semi-finals.
His club career hasn't lived up to the same heights, though.
The wide forward managed only three goals in 28 total appearances for Sporting last season and has scored only 25 times in 200 club games to date in what has been a stop-start existence.
A statement from Arsenal read, "We would like to wish Joel well for his time in Spain."
Out of favour forward Lucas Perez had earlier left Arsenal on loan for Deportivo on deadline day, while Alex Oxlade-Chamberlain traded north London for Merseyside in a £35m move to Liverpool.
Lucas Perez has officially left Arsenal on loan to rejoin former club Deportivo La Coruna for the duration of the 2017/18 season.
Perez joined the Gunners from Deportivo in a £17m deal last summer but failed to establish himself in Arsene Wenger's plans. As such, the Spaniard played only 11 Premier League games.
He did, however, score when given opportunities in the FA Cup and Champions League, contributing six goals in 10 games in those competitions.
During the summer, Perez saw his number nine jersey handed to new signing Alexandre Lacazette, seemingly signalling that he had been deemed surplus to requirements.
After something of a journeyman existence earlier in his career, Perez had been prolific during the 2015/16 season with Deportivo. He netted 17 times in 36 La Liga games and was the fourth highest Spanish scorer in the division behind only Aritz Aduriz, Ruben Castro and Borja Baston.
Arsenal have wished the 28-year-old luck on his loan.
A statement read, "We all wish Lucas well for his time with Deportivo this coming season."
Liverpool have confirmed that striker Divock Origi has completed a season-long loan move to Wolfsburg.
The deal, which will see the Belgium international spend the 2017/18 campaign in the Bundesliga, includes a reported loan fee of £6m for the temporary move.
The 22-year-old remains highly rated by the Liverpool management, but the club couldn't provide guarantees over his game time this season, with the player's father even publicly suggesting his son needed to move.
After an impressive World Cup, Origi joined the Reds in 2014, but after a season back on loan with Lille, struggled to earn a regular place in the starting lineup with Roberto Firmino the preferred centre forward under Jurgen Klopp.
The Belgian, who could make his debut for his new side on September 9 at home to Hannover 96, has scored 21 goals in 77 appearances for Liverpool in total.
Liverpool insisted on a clause allowing them to recall Divock Origi from Wolfsburg in January if necessary— paul joyce (@_pauljoyce) August 31, 2017
Liverpool fans and Jurgen Klopp will be keeping a keen eye on Origi's exploits this season in the hope he can return to Anfield a more developed striker, after a season of first team football in one of Europe's top leagues.
Manchester City have confirmed that Belgian international Jason Denayer has left the club to join Galatasaray on a season-long loan deal.
The 22-year-old is a serial loanee who has spent the last three seasons away from the Etihad Stadium on temporary deals. Denayer has spent time at Celtic and Sunderland, as well as with Galatasaray in a previous loan spell.
The Belgian international made 28 appearances for the Turkish giants during his previous spell with Galatasaray, in 2015/16, and assisted the goal that won the cup final against Fenerbahce.
Denayer has made eight appearances for the Belgian national team, and will hope that regular football in Turkey will catch the eye of Roberto Martinez, should the Red Devils qualify for the 2018 World Cup in Russia.
Denayer has never made a professional appearance for City, despite being one of the club's highest rated talents in the academy between 2013 and 2015.
The centre-back was one of a couple of unwanted centre-backs in Pep Guardiola's squad, with Eliaquim Mangala also being touted to the likes of Crystal Palace and West Brom. If Mangala leaves, Jonny Evans could finally arrive from the latter.
Borussia Dortmund have confirmed the signing of Manchester City youngster Jadon Sancho, bringing the wantaway 17-year-old in for just £170,000.
The City star is yet to make his senior club debut but has built a reputation for himself in the youth system, winning the Golden Ball at the European Under-17 championships. Sancho netted five goals at the championships, while assisting another five.
Thought to be frustrated by a lack of game time at the Etihad, with no clear route into the first team, Sancho rejected a new deal in Manchester this summer to force a move away.
Tottenham were thought to be in the driving seat in the chase for the youngster up until Thursday, before a small host of European clubs overhauled them.
Real Madrid and RB Leipzig both came in for the 17-year-old at the last minute, but it was Peter Bosz's side who won the race - tying up the future of the exciting young English forward - who will surprisingly wear the number seven shirt recently vacated by Ousmane Dembele.
Dortmund have recruited well this summer, completing deals for Andrey Yarmolenko, Maximilian Philipp, Mahmoud Dahoud, Jeremy Toljan and Omer Toprak as they look to challenge Bayern Munich for the German title once again this season - sitting top of the table after two games.
Serie A side Hellas Verona have completed the signing of Barcelona youngster Seung-Woo Lee on a four-year deal, although the Spanish club have included a buy-back clause in the deal.
According to Hellas Verona's official website, the buy back clause in Lee's contract is valid for the first two years of the contract, and is a smart move by the Copa del Rey champions as the 19-year-old is considered a bright prospect for the future.
The South-Korean would, under normal circumstances, still be a Barcelona player, except for the fact that the Spanish club have already filled their two non-EU spots in their Barcelona B side.
As a result of this, Lee has been shipped out to the Italian side as a way to gain the promising talent some valuable game time and experience, whilst the buy back clause also enables Barcelona to bring him back should a non-EU space become available in the next two years.
The South-Korean becomes the second precocious talent to leave the Nou Camp this summer, following the departure of 18-year-old Jordi Mboula to Monaco on a five-year deal.
Barcelona are still hoping to follow up their club-record capture of Ousmane Dembele with the signing of Liverpool outcast Philippe Coutinho as the deadline draws ever closer, although the Merseyside club remain adamant that the Brazilian international will not be leaving Anfield this summer.
Liverpool are reportedly in advanced talks to sign Monaco's Thomas Lemar, and Barcelona have also joined the race for the Frenchman in what appears to be a retaliation to the Premier League club's firm stance over Coutinho.
Leicester City have officially completed the signing of Austrian international defender Aleksandar Dragovic from Bayer Leverkusen on loan until the end of the season.
The Foxes have described Dragovic as a 'commanding and imposing authority in central defence' and he will link up with his new team-mates for the first time after the current international break.
The 26-year-old has been linked with various Premier League clubs in the past, including Manchester United and Arsenal, and established a sound reputation for himself during spells at Basel and Dynamo Kyiv.
It would appear that his time in Germany hasn't quite gone according to plan, having only made the move to Leverkusen last summer, but is still be considered a quality acquisition for Leicester.
Dragovic has previously won league titles in both Switzerland and Ukraine and has played Champions League football for each of his last three clubs.
With Robert Huth and club captain Wes Morgan both ageing, Leicester fans may expect to see a potential partnership between Dragovic and £17m signing Harry Maguire at the heart of the defence on occasion this season.
Stoke City have confirmed they have agreed to a deal with Toulouse for them to take midfielder Giannelli Imbula on a season-long loan.
The Frenchman has failed to live up to his billing so far at the Bet365 Stadium after signing from Porto for a club-record fee of £18.3m in the winter window of 2016.
He started brightly under Mark Hughes but soon faded, and struggle to dislodge the likes of Joe Allen, Glenn Whelan and Charlie Adam from the starting XI last season.
The new campaign saw him fail to feature once again, and so the Potters have allowed him to leave temporarily in order to get back playing regular first team football.
The Belgium-born midfielder started out in Ligue 1 with Guingamp, the team where he made his name, before switching to Marseille in 2013.
He joined Porto in 2015 and spent a solitary season there before Hughes and Stoke came calling with a club-record bid. His latest move means he has now had five clubs in as many years.
Stoke fans could also be bidding goodbye to his teammate Bojan before the 11pm deadline - the Spaniard has been linked with a move to La Liga side Deportivo Alaves and is seemingly unfancied by Hughes, who sent him out on loan to Mainz for the second half of last season.
Brighton & Hove Albion have confirmed the signing of goalkeeper Tim Krul from Newcastle on a season-long loan deal.
The Dutch international travelled to the south coast on Thursday afternoon before completing the transfer in the evening.
Krul, who has made 157 appearances for Newcastle in the Premier League, joined Ajax on loan last season, and spent the second half of the campaign at AZ Alkmaar, helping them to sixth place in the Eredivisie.
Brighton manager Chris Hughton claimed that the 29-year-old will prove a valuable addition to the squad of the newly-promoted Seagulls.
“I know Tim from my time at Newcastle and he is an excellent professional that has a vast amount of experience at both club and international level," Hughton said.
“He’s played an extensive amount of games in the Premier League, as well as playing in the Europa League and his experience will also help benefit the other keepers in the squad.”
Den Haag-born Krul, who moved to Tyneside at the age of 17, had fallen out of favour under Magpies boss Rafa Benitez.
The former Falkirk and Carlisle United loanee will now provide competition for fellow summer recruit Matthew Ryan at Brighton.
Watford have completed the signing of Udinese goalkeeper Orestis Karnezis on a season-long loan deal.
The Club confirmed the news on their website on Thursday afternoon, meaning the 32-year-old will join up with the Hornets squad after the international break as he is in action for Greece.
Karnezis has been brought in to provide Heurelho Gomes and Daniel Bachmann with competition for the number one shirt as Marco Silva is looking to add more depth to his side, who have started of the season impressively and are currently unbeaten.
The Greek joined Udinese from Granda in 2014 and has featured 110 times for the Serie A club, as well as being capped 42 times for his national team.
He has played in Europe for Panathinaikos where he won the Best Goalkeeper Award in 2012 and had been linked with a move to Newcastle, but Watford have beaten the Magpies to the experienced stopper.
His move means that Costel Pantilimon is now free to leave Vicarage Road and the Romanian has been linked with a move to West Brom as Tony Pulis is looking to provide Ben Foster with competition.
Karnezis is the Hornets 11th summer signing and may well add one more before the 11pm deadline, after being linked with Udinese striker Molla Wague.
Watford have officially announced the signing of Udinese defender Molla Wague on a season-long loan deal, with the Mali international set to join Marco Silva's side after the international break.
The news broke on the club's official website, and the 26-year-old becomes the Hornets' 11th capture of the summer, and further reinforces the London side's defensive ranks as the look to break into the top ten.
The centre-back began his career at French side Caen, and has amassed 25 caps for Mali since debuting back in 2013.
Wague spent time on loan at Leicester last season, but only managed to make one appearance in the FA Cup, in which he dislocated his shoulder.
Watford look to have completed their business for this summer, barring any late surprises.