The America's Cup, informally known as the Auld Mug, is a trophy awarded in the sport of sailing. It is the oldest international competition still operating in any sport. America's Cup match races are held between two sailing yachts: one from the yacht club that currently holds the trophy (known as the defender) and the other from the yacht club that is challenging for the cup (the challenger). Matches are held several years apart on dates agreed between the defender and the challenger. There is no fixed schedule, but the races have generally been held every three to four years. The most recent America's Cup match took place in March 2021.The cup was originally known as the 'R.Y.S. £100 Cup', awarded in 1851 by the British Royal Yacht Squadron for a race around the Isle of Wight in the United Kingdom. The winning yacht was a schooner called America, owned by a syndicate of members from the New York Yacht Club (NYYC). In 1857, the syndicate permanently donated the trophy to the NYYC, under a Deed of Gift that renamed the trophy as the 'America's Cup' after the first winner and required it be made available for perpetual international competition.

Any yacht club that meets the requirements specified in the deed of gift has the right to challenge the yacht club that currently holds the cup. If the challenging club wins the match, it gains stewardship of the cup. From the first defence of the cup in 1870 until the twentieth defence in 1967, there was always only one challenger. In 1970 multiple challengers applied, so a selection series was held to decide which applicant would become the official challenger and compete in the America's Cup match. This approach has been used for each subsequent competition. The Prada Cup (known as the Louis Vuitton Cup from 1983 to 2017) is awarded to the winner of the challenger selection series.

The history and prestige associated with the America's Cup attracts the world's top sailors, yacht designers, wealthy entrepreneurs and sponsors. It is a test of sailing skill, boat and sail design, and fundraising and management skills. Competing for the cup is expensive, with modern teams spending more than $US100 million each; the 2013 winner was estimated to have spent $US300 million on the competition.The trophy was held by the NYYC from 1857 until 1983. The NYYC successfully defended the trophy twenty-four times in a row before being defeated by the Royal Perth Yacht Club, represented by the yacht Australia II. Including the original 1851 victory, the NYYC's 132-year reign was the longest (in terms of time) winning streak in any sport.Early matches for the cup were raced between yachts 6590 ft (2027 m) on the waterline owned by wealthy sportsmen. This culminated with the J-Class regattas of the 1930s. After World War II and almost twenty years without a challenge, the NYYC made changes to the deed of gift to allow smaller, less expensive 12-metre class yachts to compete; this class was used from 1958 until 1987. It was replaced in 1990 by the International America's Cup Class, which was used until 2007.

After a long legal battle, the 2010 America's Cup was raced in 90 ft (27 m) waterline multihull yachts in Valencia, Spain. The victorious Golden Gate Yacht Club then elected to race the 2013 America's Cup in AC72 foiling, wing-sail catamarans and successfully defended the cup. The 2017 America's Cup match was sailed in 50 ft foiling catamarans, after legal battles and disputes over the rule changes.The America's Cup is currently held by the Royal New Zealand Yacht Squadron, who successfully defended the 36th America's Cup in March 2021 using an AC75 foiling monohull called Te Rehutai, owned and sailed by the Team New Zealand syndicate. The next America's Cup will be held between the Royal New Zealand Yacht Squadron and the Royal Yacht Squadron, at a date to be determined. Both the 37th and 38th America's Cup matches will be sailed in AC75 class yachts.

Australia II (KA 6) is an Australian 12-metre-class America's Cup challenge racing yacht that was launched in 1982 and won the 1983 America's Cup for the Royal Perth Yacht Club. Skippered by John Bertrand, she was the first successful Cup challenger, ending a 132-year tenure (with 26 successful defences) by the New York Yacht Club.