There have been plenty of big transfers down the years, but how many of them had a lasting legacy? Here are 10 of the most pivotal and influential transfers in football history ...
10) Yaya Toure to Manchester City, 2010
In the years after they were taken over by Sheikh Mansour's Abu Dhabi United Group in 2008, Manchester City signed a number of significant players: David Silva, Sergio Aguero and Carlos Tevez were all fine additions, but ultimately Yaya Toure was the man who became the fulcrum of the City team.
Signed from Barcelona for around €30m, he scored the winners in the semifinal and final of the 2010-11 FA Cup, City's first trophy in 35 years; he was the key man down the stretch as they recovered to win their first Premier League title in 2012; he got 20 goals from midfield as City won it again in 2014. Toure was the signing that showed City meant business, that they weren't just buying the shiniest and showiest players, but ones that would make them win.
9) Zlatan Ibrahimovic to Barcelona/Samuel Eto'o to Inter, 2009
Ibrahimovic arguably won a couple of league titles for Inter Milan on his own, his influence was so strong under Roberto Mancini and then Jose Mourinho that the rest of the team (and sometimes the manager) turned to him to fix things when it was all going wrong. That isn't necessarily a bad thing, but it can be: so when Barcelona offered them around €46m plus Samuel Eto'o in 2009, it was an opportunity to create a team, rather than 10 guys plus Zlatan. And it worked out pretty well, Inter winning the first and only treble in Italian football history. For his part, Ibrahimovic won five trophies at Barca but left after just over year following a much-publicised bust-up with manager Pep Guardiola.
8) Zinedine Zidane to Real Madrid, 2001
The Luis Figo deal might have made a bigger splash in the early years of Florentino Perez's first Galactico project in 2000, but players had moved between Barca and Real before and the Portuguese was merely excellent during his time at the club.
After signing from Juventus a year later for a world-record 150 billion lire (around €77.5m with a fixed exchange rate), Zidane would become one of Real's greatest ever, consistently able to come up with a moment of genius to win a trophy, and then one of their greats off it too. Debate will rage about the now-Real Madrid boss's tactical nous or otherwise, but when you've won three straight Champions Leagues you can ignore any debate you like.
7) Gianluigi Buffon to Juventus, 2001
The Zidane deal was extra significant because of what it meant for the selling club, too. The idea of selling a star and buying a team is one of those theories that usually doesn't work, but it emphatically did for Juventus: they used the money from Zidane to recruit Buffon and Lilian Thuram from Parma for €52m, as well as spending around €38m on Lazio's Pavel Nedved. Juve finished top of Serie A in four of the next five seasons, and while the Calciopoli scandal saw two titles stripped and the club relegated to Serie B, Buffon stayed, and did so for the better part of two decades to become a legend.
6) Neymar to PSG, 2017
Perhaps it's too early to judge the long-term ramifications of this world-record transfer, but it's arguably the move that had the biggest ripple effect throughout football, certainly in the last few years. More than doubling the transfer record Man United broke to sign Paul Pogba from Juventus for €105m, PSG paid Neymar's €222m release clause, which Barcelona quickly spent on Ousmane Dembele (€105m) from Dortmund and Philippe Coutinho (€120m) from Liverpool. The Reds used that cash to buy Virgil van Dijk (€84.5m) and Alisson (€62.5m), shoring up their defence and making them European champions and the dominant team in the Premier League. Of course the idea was that the move would have a transformative effect on PSG, not Liverpool, but there's still time for that we suppose.
5) Alfredo Di Stefano to Real Madrid, 1953
Di Stefano's move to Real Madrid might be the transfer about which there are the most stories to be told in football history. He was initially supposed to sign for Barcelona, but it was a move that involved four clubs (Colombia's Millonarios and Argentina's River Plate, as well as Real Madrid and Barcelona), various contradictory deals struck by intermediaries, a proposed arrangement whereby he would represent Real and Barca in alternate seasons and, allegedly, the intervention of Spanish dictator General Franco.
Of course Di Stefano eventually joined Real and a period of historic dominance ensued: the club won eight league titles and five European Cups, among others. The course of European football history could have been so different if he had gone to Catalonia instead.
4) Eric Cantona to Manchester United, 1992
The story of how Manchester United came to buy Cantona has often been told: Leeds United's chairman Bill Fotherby called United to ask about buying full-back Denis Irwin but ending up selling probably the most charismatic player ever to appear in the Premier League. Cantona was the final piece in Sir Alex Ferguson's first great United team, the man who helped turn them from chokers to champions, helping them land five titles and two FA Cups, while teaching the kids from the Class of '92 how to be men before his exit in 1997. United might have still been a good team in the 1990s without Cantona, but they wouldn't have dominated like they did.
3) Diego Maradona to Napoli, 1984
Maradona was damaged goods in 1984. After two chaotic years with Barcelona in which he was known more for his off-pitch shenanigans than his play, he was desperate to leave but there wasn't a queue of clubs waiting to take him.
Napoli were a moderate but ambitious club, who nearly bankrupted themselves in finding the 13bn lire ($10m) it cost to recruit him, but it was worth every penny. Maradona became not just Napoli's greatest ever player but an icon, leading them to their only two Serie A titles, a Coppa Italia and a UEFA Cup. They may win another Serie A, but they will never know times like that again.
2) Kenny Dalglish to Liverpool, 1977
Legendary Liverpool manager Bob Paisley probably didn't realise it at the time, but when he paid Celtic a then-British record fee of £440,000 for midfielder Kenny Dalglish in 1977, he was not only buying the man who would be the driving force behind three European Cup and four league title wins on the pitch, not only the man who would win three further league titles as a manager, but a man who would become the soul of an entire football club.
Dalglish was Liverpool's north star who guided them through perhaps the darkest time any team has ever suffered, after the Hillsborough tragedy in 1989. Paisley bought a player, but got a deity.
1) Johan Cruyff to Barcelona, 1973
Most of the time, the best a club can hope for from a big transfer is that the player doesn't embarrass them. In a few cases they turn out to be brilliant; in even fewer, they exceed expectations. But Cruyff established a club philosophy that has lasted more than 30 years.
After making history with Ajax and Netherlands' "Total Football," his 6m guilder ($2m) move from the Amsterdam club set in motion a series of events that made Barcelona one of the most dominant in European football for generations. He won just a single La Liga and Copa del Rey title at Camp Nou as a player, but returned as manager in 1988 to land four more titles and the European Cup. The world-famous youth system at La Masia that would produce some of the greatest the game has ever seen was down to Cruyff; the tiki taka style of attacking football based on possession; the training methods; the winning mentality. He was the bargain of the century.