As mandated by FIFA regulations, the transfer window is the registration period during which clubs can transfer players from other teams into their own.
For most major European leagues (which start around August - September, and end in May, there are two such windows, the longer one between the end of a season and the commencement of the next one, and the shorter one in the middle of the season.
Usually, the summer transfer window is a period of busy activity for major European clubs. The summer transfer window in 2019-20, which closed on 2nd September 2019 in Italy, Spain, Germany, and France (the English window closed on 8th August 2019), was no different and saw a spate of high profile transfers in European club football.
English clubs were the busiest during this period, leading the way with €1.54 billion (£1.4 billion). Juventus, Napoli, Roma, and the two Milan clubs shelled out a combined €690 million while in the Bundesliga, Bayern and Dortmund got poorer by €271 million.
The top-three clubs in Spain (Real Madrid, Barcelona, and Atletico) hauled in summer reinforcements for a combined €806 million. Real Madrid had the most transfer outflow (€307.5 million) for a club during this period.
Midfielders were the flavour of the summer, with the top 25 transfers during this period involving 10 midfielders. Here is a preview of the 10 most expensive summer acquisitions of the season, which features an eclectic ensemble of three strikers, four midfielders, and three defenders:
#10 Romelu Lukaku (€65 million)
Romelu Lukaku moved from Manchester United to Serie A club Internazionale for 65 million Euros. The 26-year-old Belgian centre-forward arrives in Italy after scoring 33 goals in the Belgian League (Anderlecht) and 113 goals in 9 seasons in the English Premier League (Everton-68, Manchester United-28, and West Ham-17).
Inter were scouting for a reliable striking option after protracted contract negotiations with their erstwhile captain Mauro Icardi who fell out of favour with the club faithful and eventually joined PSG on a loan deal. In Lukaku, Inter seems to have found a like-for-like replacement as the Belgian announced his arrival in Italy with goal scoring debut.
#9 Rodrigo Hernández (€70 million)
Rodrigo Hernández, also known as Rodri, is the third-most-expensive acquisition by a Premier League club this summer. Manchester City triggered Rodri's release clause by shelling out a club-record €70 million (£62.8 million) to Atlético Madrid.
The 23-year-old Spanish defensive midfielder arrives in England after four seasons in the Primera Liga (3 seasons with Villareal and 1 season with Atlético).
#8 Frenkie de Jong (€75 million)
The highly-rated 22-year-old central midfielder was snapped up by defending La Liga champions Barcelona for €75 million after a stellar European season with Ajax.
Frenkie de Jong is adept in a variety of midfield roles (defensive, central, holding, box-to-box) and also as a centre-back. The young Dutchman who is renowned for his brilliant positional sense, clean tackling and ability to start attacks, starred prominently during Ajax's fairytale run from the qualifying rounds to the semifinals in the Champions League last season.
De Jong arrives in Spain after 5 seasons in the Eredivisie for Willem II and Ajax.
#7 Nicolas Pépé (€80 million)
Nicolas Pépé's 22 goals and 11 assists last season grabbed eyeballs across Europe before Arsenal won a close race with SSC Napoli for his signature by shelling out a club-record €80 million (£72 million) to Lille for the services of the Ivory Coast midfielder.
After Napoli had also agreed to meet Lille's valuation for the midfielder, Arsenal's higher wage offer tipped the balance in favour of the Gunners.
Pépé arrives in England after three seasons in the French Ligue 1 where he scored 3 goals for Angers and 35 goals for Lille. The midfielder was the top scorer behind Kylian Mbappe (33 goals) in Ligue 1, scoring 22 goals for Lille, which included a hattrick in an away game at Amiens.
The 24-year-old's pace, close control, and directness are known to harangue the best of opposition defenders.
#6 Lucas Hernández (€80 million)
Serial Bundesliga winners Bayern Munich acquired the services of French centre-back Lucas Hernández from Spanish club Atletico Madrid for a Bundesliga record €80 million.
The versatile 23-year-old 2018 World Cup winner for France, who can play at both centre-back and fullback positions, arrives in Germany following 5 seasons with Atletico.
#5 Matthijs de Ligt (€85.5 million)
The 20-year-old Dutch centre-back played a prominent role in Ajax's run to the Champions League semifinals last season. He scored the winner in Turin which knocked out Juventus from the quarterfinals of European club football's premier event.
The Ajax captain's exemplary leadership and stellar matchplay impressed Juventus enough to part with €85.5 million to land the services of the young centre-back, which made de Ligt the second-most expensive defender in the world and the third-most-expensive arrival in Serie A.
De Ligt's maturity beyond his age and his clean tackling, strength, accuracy of passes and prowess from setpieces make him an invaluable acquisition for the Bianconeri. At Juventus, he would have the best platform to blossom into one of the world's finest defenders.
#4 Harry Maguire (€87 million)
Harry Maguire joined Manchester United from Leicester City for €87 million (£80 million) in a deal which made Maguire the most expensive defender in the world and the most expensive acquisition by an English club this summer.
Maguire started his professional career in the Championship (English second division) with Sheffield United before moving to Hull City and Leicester City before arriving at Old Trafford.
The 26-year-old centre-back, who plied his trade in the third tier 5 seasons ago, makes up for his lack of pace by his aerial prowess, astute reading of the game and ball distribution.
#3 Eden Hazard (€100 million)
The 28-year-old attacking midfielder joined Real Madrid from Chelsea for €100 million, making him the Spanish club's most expensive signing in their history, after Gareth Bale.
Eden Hazard arrives in the Spanish capital after scoring 36 Ligue 1 goals in 5 seasons at Lille and 85 Premier League goals in 7 seasons at Chelsea, winning 2 Premier League titles, 2 Europa League titles, one FA Cup and one League Cup for the latter.
Starting as a winger at Lille, Hazard blossomed into a world-class midfielder at Chelsea, where he favoured the left flank to cut in from. The Belgian is a versatile player who can be deployed as a second striker, lone striker or a false nine and is also accurate from the penalty spot and freekicks.
#2 Antoine Greizmann (€120 million)
The 28-year-old Antoinne Greizmann was snapped up by Barcelona from Atletico Madrid for €120 million, which made the French striker Barcelona's third most expensive acquisition (behind Coutinho and Dembele).
Making his La Liga debut in 2010-11, Greizmann is an accomplished striker in the Spanish league, netting 46 goals in 4 seasons for Real Sociedad and 94 goals in 5 seasons for Atletico Madrid.
The Frenchman is a versatile left-footed forward and is capable of scoring goals from a variety of attacking positions like the main striker, attacking midfield and from the flanks.
#1 João Félix (€126 million)
The 19-year-old Portuguese striking sensation was bought by Atletico Madrid from Benfica in a club-record €126 million deal.
João Félix scored 15 goals in his lone top-flight season for Benfica and has drawn comparisons with Portuguese greats like Rui Costa and João Pinto.
The astronomical transfer fee, the most for a teenager, could, however, prove to be burdensome for the young Felix as he seeks to fill the void in the Atletico forward line after the departure of Antoinne Greizmann to Barcelona.
The teenager's keen eye for goal and passing skills have drawn comparisons with his boyhood idol Kaka and he is tipped for big things at Atletico.