They are the football stories which dominate the sports pages of newspapers Europe-wide. In fact, transfer stories and speculation often overshadow events on the pitch, providing the juicy narrative that accompanies footballing debate.
Nearly every year, though, there is at least one transfer that really captures the imagination. Whether it be caused by the relationship of the two sides involved, the standing of the player or the fee involved, there are some transfers that are particularly memorable.
Whether it was Real Madrid parting with £80 million to sign Cristiano Ronaldo, or Robin van Persie swapping Arsenal for long-term rivals Manchester United, there are some trades that were always going to provide storylines for months to follow.
But, a high-profile transfer is scant guarantee of success; Some of the biggest and most expensive transfers have proved to be spectacular failures.
Let's take a look at ten era-defining transfers of the past 10 years and assess just how successful they ultimately were.
David Beckham (Manchester United to Real Madrid, 2003); £24.5 million—SUCCESS
Perhaps the closest call to make. When Beckham joined Real Madrid in 2003, they were still very much at the top of the European game. (BBC)
However, Beckham's arrival and the policies of the Galacticos era would soon see Los Merengues surpassed by Barcelona domestically—who famously opted for Ronaldinho following a rejection from the Englishman that summer.
Beckham was a first-team regular throughout his four seasons at the Madrid club and, having been dropped by Fabio Capello following the announcement of his impending departure in 2006-07, produced some of the best form of his career to help Real regain the La Liga title once again.
This success, as well as his consistent performances and massive commercial benefit to the club, probably tip the scales in favour of success.
Wayne Rooney (Everton to Manchester United, 2004); £27 million—SUCCESS
When Rooney joined Manchester United following an explosive Euro 2004 (BBC), it was expected that he would become one of the very best players in the world.
While he arguably hasn't hit those heights in the nine years since, there can be little doubt that Rooney has played a major role in the continued power of the Red Devils, both domestically and continentally.
The England international could notch his 200th goal for the club before this season is up, and has done so at a rate of a goal every other game.
A haul of five Premier League titles, a Champions League and a Club World Cup, as well as a selection of domestic cups, would suggest that the 2009-10 Premier League Player of the Year has been an undisputed success.
Andriy Shevchenko (AC Milan to Chelsea, 2006); £30 million—FAILURE
The most famous of Roman Abramovich's personally sought-after transfers, Andriy Shevchenko arrived in West London in 2006 off the back of seven highly successful years in Italy with AC Milan.
The Ukranian's arrival, though, was one of the catalysts of the downfall of the Mourinho era. Within months, the Portuguese manager was out the door. Shevchenko, clearly, had not been the manager's choice of signing.
Signing a 30-year-old for such a sizable fee was always going to be a major risk, but a return of just nine goals in 48 Premier League games before his eventual departure fell far below anybody's initial expectations.
Even a loan return to his San Siro home failed to help Shevchenko recover form, and by 2009, he was allowed to leave the club to rejoin Dinamo Kiev.
Robinho (Real Madrid to Manchester City, 2008); £32.5 million—FAILURE
When he moved from Santos to European football in 2005, Robinho was hailed as the potential "Next Big Thing" of Brazilian football. Thus, when he forced a move to the Premier League three years later (BBC), it was supposed to be a big moment for both Manchester City and English football.
Robinho began life in England in fine style, quickly scoring goals on a regular basis for his ambitious new side. However, such form quickly dropped off in the second half of his first campaign.
Injury struck at the beginning of his second season at the club, and a change of manager saw him fall further down the pecking order after some distinctly average performances.
The Selecao star, known for his flamboyant dribbling, would eventually move on, with Santos offering a six month loan deal. That summer, upon his return, he would permanently leave the club in a £15 million move to AC Milan—a loss of £17.5 million in just two years. (ESPN)
Kaka (AC Milan to Real Madrid, 2009); £56 million—FAILURE
Brazil international Kaka was the World Player of the Year in December 2007, and just 18-months later was on the move to Real Madrid for a new world record fee of £56 million. (Telegraph)
The elegant attacking midfielder, though, has never come close to repeating his Milan form in the Spanish capital. After a decent opening campaign, an injury delayed his start to the 2010-11 season, and the signings of Mesut Ozil and Angel Di Maria further limited his playing time.
Since that post-2010 World Cup surgery, the Brazilian has endured several false-starts at the Bernabeu, showing signs of recovering form before picking up further injury concerns.
While his side were celebrating a first La Liga title of the second Florentino Perez era in 2012, Kaka, sadly, was being heavily linked with cut-price moves away from the club. He is yet, though, to find a new home.
Cristiano Ronaldo (Manchester United to Real Madrid, 2009); £80 million—SUCCESS
That same summer, Real Madrid would once again smash the world transfer record in bringing Portuguese winger Cristiano Ronaldo to the Santiago Bernabeu for an astonishing £80 million. (BBC)
His impact in Spain has been nothing short of astonishing, and had it not been for the equally phenomenal Lionel Messi at Barcelona, there is no doubt that it would be Ronaldo being compared to the game's very greatest players.
The forward is now coming up to 200 goals in the famous white shirt, and will do so scoring at a rate of around a goal per game over a four year period. These are goalscoring feats that, Messi aside, no one has come close to in Europe's major leagues, in recent years.
The former Manchester United player was a major component of Real Madrid ending Barcelona's grip on La Liga in 2011-12, and will no doubt hope for further success before he eventually moves on from the club.
Zlatan Ibrahimovic (Inter Milan to Barcelona, 2009); £57 million—FAILURE
When Swedish superstar Zlatan Ibrahimovic joined Barcelona for a fee that amounted to £57 million, including Cameroonian striker Samuel Eto'o, he was intended to be the Catalan giants' long-term attacking focal point. (Guardian)
However, just a year later, as Eto'o was celebrating playing a major role in Inter's capture of the Champions League title, Ibrahimovic was already being offered a route away from the Camp Nou.
What had gone wrong? While the Swede's scoring rate in Spain was far from poor, it was clear that he was not wanted as part of the Guardiola regime. The rise of Messi and Ibrahimovic's somewhat selfish style both clearly influenced the manager's thinking.
In 2010, he would join Italian side AC Milan on an initial loan deal. (BBC) After a successful return to the San Siro, the move would be made permanent in 2011 for £20 million—a £37 million loss.
Fernando Torres (Liverpool to Chelsea, 2011); £50 million—FAILURE
A British record fee and a five-and-a-half year contract should buy somewhat of a guaranteed investment. (BBC) For Chelsea, though, Spain striker Fernando Torres has proved an abject failure.
The Spain star joined Abramovich's side while out of form. Liverpool fans will tell you that he had been playing for a move, but it is clear that the club were not going to reject £50 million for his services.
The former Atletico Madrid striker had consistently scored in his three-years in the North-West, but would add just one goal in his first six months in London. His ability to recapture old form was already being questioned.
His spell at Chelsea is now two-and-a-half years old, and he is more famed for goal droughts that have spanned over 10 hours at a time than goalscoring. Just 14 Premier League goals in 78 appearances is not the return of a man with his price tag.
Rumours have consistently linked Torres with a move away from the Blues, having been replaced as first choice by Demba Ba in January 2013. It is likely, though, that the club would have to accept a massive loss to offload their star forward.
Sergio Aguero (Atletico Madrid to Manchester City, 2011); £38 million—SUCCESS
Argentine forward Sergio Aguero added another true superstar to Manchester City's ranks when he joined ahead of the 2011-12 season, and proved decisive in a memorable title success in his first season.
Aguero enjoyed the best league campaign of his career thus far upon arrival in England, scoring 23 goals to secure the league title for his side—including the goal that clinched success in injury time on the final day of the season.
While he will be disappointed with his return this campaign, it is fair to say that his initial contributions already mean that his Manchester City career will forever be remembered as a success. At 24, his valuation can only have risen since arriving at the club.
The next stage for Aguero and his City side is clearly to make an impact in European competition. Whether that happens or not, though, he will forever be close to the hearts of the club's loyal fans for that one moment last May.
Robin van Persie (Arsenal to Manchester United, 2012); £24 million—SUCCESS
While it may have been far from the most expensive transfer of the 2012 summer transfer window, Manchester United's purchase of Robin van Persie from long-term rivals Arsenal was certainly the most noteworthy. (BBC)
The Dutch forward had been Premier League top-scorer in 2011-12 before moving to Old Trafford, and looks set to repeat the feat this season—having already secured a first league title of his career.
Many have described van Persie as being the key to Manchester United's title success, and, given how it appeared rivals City would dominate the scene for some time, that is worth much of his transfer fee alone.
So successful has he been that many fans are now willing to consider the departure of Wayne Rooney for pastures new. Such thinking would have been out of the question 18 months ago, but van Persie has truly changed the balance of power both at United and in the Premier League title race.