The 2021 Australian Football League finals series was the 125th annual edition of the VFL/AFL finals series.

The series was played over five weeks in August and September, culminating in the 2021 AFL Grand Final. The top eight teams from the 2021 AFL Premiership season qualified for the finals series. AFL finals series have been played under the current format since 2000.

Due to ongoing COVID-19 restrictions, many clubs played home finals outside their home states for the second consecutive season. The New South Wales venues were unavailable because of a large outbreak in Sydney which precluded interstate travel through the state, and both Sydney clubs had been based outside the state for the last two months of the home-and-away season. The Victorian venues were available despite a smaller outbreak in the state, having hosted home-and-away matches behind closed doors right up to the end of the season, while 'sterile corridor' arrangements were in place to enable interstate travel. However, the league preferred to schedule finals which could be attended in a neutral state rather than behind closed doors in a home state, resulting in no matches being staged in Victoria, either.^[1]

Many venues operated with a restricted spectator capacity. For the first week of finals, Adelaide Oval and University of Tasmania Stadium were only allowed up to 20,000 spectators and 10,000 spectators, respectively.^[2] For the preliminary final, the allowed capacity of Adelaide Oval was slightly increased to 26,500—50% of the venue's regular total capacity.^[3]

More information Brisbane, Adelaide ...

	Brisbane Adelaide Perth Launceston
Brisbane		Adelaide
The Gabba Capacity: 37,000		Adelaide Oval Capacity: 20,000 (reduced)
Launceston		Perth
University of Tasmania Stadium Capacity: 10,000 (reduced)		Optus Stadium Capacity: 60,000

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The system used for the 2021 AFL finals series was a final eight system. The top four teams in the eight received the "double chance" when they play in week-one qualifying finals, such that if a top-four team loses in the first week it still remained in the finals, playing a semi-final the next week against the winner of an elimination final. The bottom four of the eight played knockout games—only the winners survived and moved on to the next week. Home-state advantage ordinarily goes to the team with the higher ladder position in the first two weeks, to the qualifying final winners in the third week, but due to the COVID-19 pandemic, some states were unable to host matches.

In the second week, the winners of the qualifying finals received a bye to the third week (as normal). The losers of the qualifying final played the elimination finals winners in a semi-final. In the third week, the winners of the semi-finals from week two play the winners of the qualifying finals in the first week. The winners of those matches move on to the Grand Final.^[4]

The finals were originally due to commence over the weekend of 3–5 September, with a bye week in place between Round 23 and the finals commencing. This bye week was conventional since 2016 and even observed in the delayed 2020 season. However, in an announcement made on 16 August, the bye week was dropped and the first week of finals was brought forward to the weekend of 27–29 August as a contingency, to allow the league to use the bye week at short notice to respond to any unforeseen changes to border or societal restrictions associated with the COVID-19 pandemic, without impacting the scheduled Grand Final date of Saturday 25 September. The bye week was ultimately observed between the preliminary finals and the Grand Final.