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Masters swimming is a special class of competitive swimming for swimmers 18 or 20 years or older (Canada, USA and Australia allow from 18 years old, while Europe allows from 20 years old). They compete within age groups of five years, determined by the swimmer's age on 31 December the year of the competition (in U.S. for meets held in non-metric pools, the age is determined as of the day of the competition):
Age Groups for individual events: A:25–29 (years old), B:30–34, C:35–39, D:40-44; E:45-49; F:50-54, G:55-59; H:60-64, I:65-69, J:70-74; K:75-79; L:80-84, M:85-89, N:90-94, P:95-99 and so on at 5-year increments as necessary.
The rules and distances are nearly the same as for senior swimming. However, meet programs include 2 mixed (2 men/2 women) relay events in addition to the men's and women's relay events.
Age groups for the relay events is determined by the combined age of the team participants, allowing for swimmers of very different ages to compete together: A:100–119 (years old combined), B:120–159, C:160–199, D:200-239, E:240-279, F:280-319, G:320-359 and so on at 40-year increments as necessary.
Masters swimming is a fast-growing leisure activity, particularly in North America and Australia but also in Europe. Most towns or cities now have masters clubs. Typically these are very friendly and welcome newcomers. The minimum requirements to join a masters club vary widely, anywhere from the ability to swim one length of the pool to the ability to swim a kilometre without stopping. Club members will follow a set of different drills and swims each time typically covering anything from 1.5 km to 3.5 km. Each club will have lanes and so whilst the younger and faster swimmers who are competing nationally and regionally are at one end, the other lanes are for hobbyists who may have taken up swimming quite recently.
United States Masters Swimming is the governing body of masters swimming in the United States, sponsoring competition at all levels. In addition, it sponsors programs for non-competitive "fitness" swimmers who train primarily for the health benefits that the activity offers to the aging athlete. Masters Swimming Canada is the governing body of masters swimming in Canada, listing swim clubs, competitions and provincial master swim associations.
FINA World Masters Championships
- 1978 – Christchurch, NZL (non-FINA)
- 1984 – Toronto, CAN (non-FINA)
- 1986 – Tokyo, JAP
- 1988 – Brisbane, AUS
- 1990 – Rio de Janeiro, BRA
- 1992 – Indianapolis, USA
- 1994 – Montreal, CAN
- 1996 – Sheffield, ENG
- 1998 – Casablanca, MOR
- 2000 – Munich, GER
- 2002 – Christchurch, NZL
- 2004 – Riccione, ITA
- 2006 – Stanford, USA
- 2008 – Perth, AUS
- 2010 – Göteborg/Borås, SWE
- 2012 – Riccione, ITA
- 2014 – Montreal, CAN 
Like in senior swimming, there are world records for masters swimming, but they can only be set in a sanctioned masters meet. Masters swimming records are available at the FINA website masters section.
- "FINA General Masters Rules". FINA. Retrieved 13 June 2011.