Jacek Waldemar Bak (Polish pronunciation: ['jats?g 'b??k]; born 24 March 1973) is a retired Polish footballer who played as a central defender.
Other than his country, he competed professionally in France, Qatar and Austria, notably appearing in more than 150 competitive games for Lyon and contributing to win the 2002 national championship.
Bak represented Poland for 15 years, appearing for the nation in two World Cups and Euro 2008.