This is a list of Portuguese football transfers for the summer of 2021. The summer transfer window will open 1 July and close at midnight on 31 August. Players may be bought before the transfer windows opens, but may only join their new club on 1 July. Only moves involving Primeira Liga clubs are listed. Additionally, players without a club may join a club at any time.
The 2016–17 season is Chaves' fourteenth season in the top flight of Portuguese football. This marked Chaves' return to the Portuguese top tier, after a seventeen-year absence.
The 2017–18 season is Chaves' fifteenth season in the top flight of Portuguese football.
The 2018–19 season is Chaves' 16th season in the top flight of Portuguese football.
The 2020–21 season was Futebol Clube do Porto's 111th competitive season and 87th consecutive season in the top flight of Portuguese football. In addition to the domestic league, Porto participated in this season's editions of the Taça de Portugal, the Taça da Liga and the UEFA Champions League. The season started on 19 September 2020 and concluded on 19 May 2021.
The 2020–21 Sport Lisboa e Benfica season was the club's 117th season in existence and its 87th consecutive season in the top flight of Portuguese football. This season, Benfica invested €105 million amid the COVID-19 pandemic, a record investment in Portuguese football. Domestically, Benfica lost the Supertaça Cândido de Oliveira match, were eliminated in the semi-finals of the Taça da Liga, finished third in the Primeira Liga – their worst league position since 2008–09 – and lost a Taça de Portugal final for a second time in a row. Internationally, Benfica were eliminated in the UEFA Champions League third qualifying round and in the round of 32 of the UEFA Europa League, respectively. The season started on 18 September 2020 and concluded on 23 May 2021. Considered a failed, disastrous season, it was the first time Benfica ended trophyless since 2012–13.
The 2020–21 Boavista F.C. season was the club's 118th season in existence and the club's seventh consecutive season in the top flight of Portuguese football. In addition to the domestic league, Boavista participated in this season's edition of the Taça de Portugal, being eliminated in the fourth round. The club did not qualify for the condensed version of the Taça da Liga this season. The season covered the period from July 2020 to 30 June 2021.
The 2021–22 season was the 128th season in the existence of FC Porto and the club's 88th consecutive season in the top flight of Portuguese football. In addition to the domestic league, Porto participated in this season's editions of the Taça de Portugal, the Taça da Liga, the UEFA Champions League and the UEFA Europa League.
The 2021–22 season was the 101st season in the existence of S.C. Braga and the club's 26th consecutive season in the top flight of Portuguese football. In addition to the domestic league, Braga participated in this season's editions of the Taça de Portugal, the Taça da Liga, the Supertaça Cândido de Oliveira and the UEFA Europa League.
The 2021–22 season is the 72nd season in the existence of Boavista F.C. and the club's third consecutive season in the top flight of Portuguese football. In addition to the domestic league, Boavista F.C. participated in this season's editions of the Taça de Portugal and the Taça da Liga.
The 2021–22 season was the 72nd season in the existence of F.C. Arouca and the club's first season in the top flight of Portuguese football. In addition to the domestic league, Arouca participated in this season's editions of the Taça de Portugal and the Taça da Liga.
The 2022–23 season is the 72nd season in the history of F.C. Paços de Ferreira and their fourth consecutive season in the top flight. The club are participating in the Primeira Liga, the Taça de Portugal, and the Taça da Liga.