Beşiktaş Jimnastik Kulübü (Turkish pronunciation: [beˈʃiktaʃ], lit. 'Beşiktaş Gymnastics Club'), abbreviated as BJK, is a Turkish professional sports club founded in 1903 that is based in the Beşiktaş district of Istanbul. The club's football team is one of the Big Three in Turkey and one of the most successful teams in the country, having never been relegated to a lower division. It was the first registered sports club in the country and one of the few that acquired the right to bear the Turkish flag on its crest.

Its football team has won 21 league titles including 16 Turkish Süper Lig, three Turkish National Division and two Turkish Football Championship titles, along with 11 Turkish Cup titles. Beşiktaş is also the only team to have won the Süper Lig undefeated, in the 1991–92 campaign. The team last won the Turkish Süper Lig title during the 2020–21 season and the Turkish Cup in the 2023-24 season. The club's home ground is Beşiktaş Stadium, a 42,590-capacity all-seater stadium located by Dolmabahçe Palace. The stadium has been considered one of the best in the world for location, design, comfort, technology, atmosphere, and transportation.

The team also participates in European competitions regularly. Beşiktaş reached the quarter-finals of the 1986–87 European Cup and displayed the best Turkish team performance in the Champions League group stage by earning 14 points and progressing undefeated in the 2017–18 campaign. Beşiktaş have also reached the UEFA Europa League quarter-finals twice, in the 2002–03 and 2016–17 seasons. Based on its UEFA coefficient, Beşiktaş is currently the 5th highest ranked Turkish team and is ranked second all-time after its rival Galatasaray.

The club's fan base, Çarşı, is well known globally. They were chosen as the best fan group in voting conducted by American sports viewers due to their 132-decibel noise record at a 2007 match against Liverpool. The group is involved with sociopolitical causes and is traditionally considered to be working-class and left-wing, supporting what is known as \"the people's team\". The highest ever football attendance in Turkish league history was recorded in a Beşiktaş-Galatasaray derby with 76,127 spectators.

The club also competes in other sports such as women's football, basketball (men's, women's and wheelchair), volleyball (men's and women's), handball, athletics, beach football, boxing, bridge, chess, gymnastics, athletics, parasports, rowing, table tennis, wrestling and esports.