Sheffield Wednesday Football Club is a professional association football club based in Sheffield, South Yorkshire, England. They compete in the EFL Championship, the second level of the English football league system.

Formed in 1867 as an offshoot of The Wednesday Cricket Club (itself formed in 1820), they were known as The Wednesday Football Club until 1929. Wednesday is one of the oldest surviving football clubs in the world of any code, and the second-oldest professional association football club in England. In 1868 its team won the Cromwell Cup, only the second tournament of its kind. They were founding members and inaugural champions of the Football Alliance in 1889, before joining The Football League three years later. In 1992, they became founder members of the Premier League. The team has spent most of its league history in English football's top two flights, though they have not played in the top tier since being relegated in 2000.

The Owls, as they are nicknamed, are one of the most successful teams in English football by major honours, having won four league titles, three FA Cups, one League Cup and one FA Community Shield. Wednesday have also competed in UEFA cup competitions on four occasions, reaching the quarter-finals of the Inter-Cities Fairs Cup in 1963. In 1991, they defeated Manchester United 1–0 in the Football League Cup final as a second-tier team. As of 2025, they remain the last team to win one of English football's major trophies while outside the top flight.

In the 19th century, they played their matches at several stadiums around central Sheffield, including Olive Grove and Bramall Lane. Since 1899, the club has played all its home matches at Hillsborough stadium, a near-40,000 capacity stadium in the north-west Sheffield suburb of Owlerton. Wednesday's biggest rivals are Sheffield United, with whom they contest the Steel City derby.