The 2020 All-Ireland Senior Football Championship is the 133rd edition of the Gaelic Athletic Association's premier inter-county Gaelic football tournament since its establishment in 1887. The public health measures introduced to combat the COVID-19 pandemic resulted in the competition being delayed. On 17 March, the GAA confirmed that the opening fixture – due to have taken place at Gaelic Park in The Bronx on 3 May – had been postponed. In June the GAA announced that the 2020 championship would be straight knock-out, the first straight-knockout since 2000. Thirty-two teams have been scheduled to take part – thirty-one of the thirty-two Counties of Ireland and London. New York were unable to participate due to travel restrictions resulting from the coronavirus pandemic. Kilkenny, as in previous years, did not enter. Initially the GAA intended to introduce the Tailteann Cup, a second-tier championship for Division 3 and 4 National Football League teams who failed to reach their provincial finals or get promoted to Division 2 of the league. The Tailteann Cup was delayed as a result of the coronavirus pandemic and will be introduced in 2021. Dublin are the defending champions.
, Leinster, Munster and Ulster each organise a provincial championship. Traditionally, some of the teams who lose a match in their provincial championship enter the All-Ireland qualifiers – New York does not enter the qualifiers. All matches are knock-out. If the score is level at the end of the normal seventy minutes, two periods of ten minutes each way are played. If the score is still level the tie goes to a replay.
All-Ireland format
The four provincial champions compete in the semi-finals. If the score is level at the end of the normal seventy minutes in a semi-final, two periods of ten minutes each way are played. If the score is still level the semi-final is replayed. If the score is level at the end of the normal seventy minutes in the final, the match is replayed.
Changes from 2019 competition
; Advanced Mark Initially trialled in the 2019 Leagues, the advanced mark rule was introduced in 2020. The referee awards a mark when a player catches the ball cleanly on or inside a 45m line from a kick in play delivered by an attacking player on or beyond the opposition's 45m line that travels at least 20m and without it touching the ground. The catching player can either signal his intent to stop and take the mark by raising an arm or continue to play on immediately. ; Sin-bin A player who commits a black card offence is sent off the pitch to the sin-bin for ten minutes. Teams are not permitted to replace the player while he is in the sin-bin, leaving them at a numerical disadvantage. If a player commits another black card offence after returning to the field he is red-carded. ; Kick-out Goalkeepers must take their kick-out from the 20 metre line. The ball must be kicked forward and all players must be 13 metres from the ball until it has been kicked. Following a motion proposed by Kildare at the GAA Congress on 28 September 2020, the kick-out rule was further modified so that an outfield player receiving a ball direct from the kick-out cannot play the ball back to their goalkeeper. Unusually, the "no back-pass" modification was not trialled before its introduction in the 2020 senior championship.
An un-seeded draw determined the fixtures for all nine teams. In April 2018 the Ulster GAA Competitions Control Committee introduced a rule that the two teams who play in the preliminary round are exempt from playing in the preliminary round in the following two years. Derry and Tyrone were therefore awarded byes to the quarter-finals in 2020 and 2021.
