Swimming at the 2020 Summer Olympics

The swimming competitions at the 2020 Summer Olympics in Tokyo were due to take place from 25 July to 6 August 2020 at the Olympic Aquatics Centre. Due to the COVID-19 pandemic, the games were postponed to 2021. However, their official name remained 2020 Summer Olympics with swimming events set for 24 July–1 August 2021 and marathon swimming set for 4–5 August 2021.

Swimming featured a record total of 37 events (18 for each gender and 1 mixed), with the addition of the men's 800 m freestyle, women's 1500 m freestyle, and the mixed 4 × 100 m medley relay.

Events
Swimming at the 2020 Olympics featured a total of 37 events (18 each for men and women and 1 mixed event), including two 10 km open-water marathons. This was a slight increase from the 34 events contested in the previous Olympic Games. The following events were contested (all pool events are long course, and distances are in meters unless stated):
 * Freestyle: 50, 100, 200, 400, 800, and 1,500;
 * Backstroke: 100 and 200;
 * Breaststroke: 100 and 200;
 * Butterfly: 100 and 200;
 * Individual medley: 200 and 400;
 * Relays: 4 × 100 free, 4 × 200 free; 4 × 100 medley (men's, women's, and mixed)
 * Marathon: 10 kilometres

Schedule
Unlike the previous Olympics, swimming program schedule occurred in two segments. For the pool events, similar to the case of the 2008 Games, prelims were held in the evening, with semifinals and final in the following morning session, spanning a day between semifinals and finals in those events with semifinals. The shift of the normal morning prelims and evening finals (to evening prelims and morning finals) occurred for these Games due to the prior request made by US broadcaster NBC (due to the substantial fees NBC has paid for rights to the Olympics, the IOC has allowed NBC to have influence on event scheduling to maximize U.S. television ratings when possible; NBC agreed to a $7.75 billion contract extension on May 7, 2014, to air the Olympics through the 2032 games and is also one of the major sources of revenue for the IOC), so that the finals from the event could be shown live in the United States.

M = Morning session, starting at 10:30 local time (01:30 UTC). E = Evening session, starting at 19:00 local time (10:00 UTC).

Swimming – individual events
FINA establishes qualifying times for individual events. The time standards consisted of two types: an "Olympic Qualifying Time" (OQT) and an "Olympic Selection time" (OST). Each country was able to enter up to two swimmers per event, provided both swimmers met the (faster) qualifying time. A country was able to enter one swimmer per event that met the invitation standard. Any swimmer who met the "qualifying" time was entered in the event for the Games; a swimmer meeting the "invitation" standard was eligible for entry, and their entry was allotted/filled in by ranking. If a country has no swimmers who meet either of the qualifying standards, it may have entered one male and one female. A country that did not receive an allocation spot but had at least one swimmer who met a qualifying standard might have entered the swimmer with the highest ranking.

Swimming – relay events
Each relay event features 16 teams, composed of:
 * 12 teams including the top-12 finishers at the 2019 World Championships in each relay event.
 * 4 teams including the 4 fastest non-qualified teams, based on times in the 15-months preceding the Olympics.

Open-water swimming
The men's and women's 10 km races featured 25 swimmers:
 * 10: the top-10 finishers in the 10 km races at the 2019 World Championships
 * 9: the top-9 finishers at the 2020 Olympic Marathon Swim Qualifier
 * 5: one representative from each FINA continent (Africa, the Americas, Asia, Europe, and Oceania).
 * 1: from the host nation (Japan) if not qualified by other means. If Japan already contained a qualifier in the race, this spot had been allocated back into the general pool from the 2020 Olympic qualifier race.

Men's events
Swimmers who participated in the heats only and received medals.

Women's events
Swimmers who participated in the heats only and received medals.

Mixed events
Swimmers who participated in the heats only and received medals.

Mixed

 * All world records (WR) are consequently Olympic records (OR).

Chinese swimming team doping controversy
On 20 April 2024, The New York Times revealed that 23 members of the Chinese swimming team tested positive for a performance enhancing drug called Trimetazidine seven months prior to the start of the games and were allowed to participate in the games with some of the swimmers winning medals. Following the publication of the report, Travis Tygart, CEO of the United States Anti-Doping Agency, accused the World Anti-Doping Agency (WADA) and the Chinese Anti-Doping Agency (CHINADA) of covering up doping by Chinese swimmers. In response to Tygart's comments, WADA stated that it “stands by the results of its rigorous scientific investigation” into the case and was “astonished by the outrageous, completely false and defamatory remarks while CHINADA stated that the reports were misleading and that the doping tests they conducted only found that the swimmers had only tested extremely low concentration of Trimetazidine which was due to contamination at the hotel they were residing at that time," although any amount of the substance constitutes a ban. In a second statement, Tygart accused both World Anti-Doping Agency and the Chinese Anti-Doping Agency for not being transparent about the findings and keeping “clean athletes in the dark”. WADA was also shown to have a double-standard as Russian figure skater Kamila Valieva tested positive for TMZ and used the same excuse, but was immediately banned for four years. On 25 April 2024, WADA announced that Eric Cottier, a Swiss attorney, would launch an independent investigation into the matter, which also drew criticism since he was hand-picked by WADA. On May 2024, WADA announced that it hold an extraordinary meeting to discuss the doping case of the Chinese swimmers.