Gregg Williams (born July 15, 1958) is an American football coach who was most recently the defensive coordinator for Tennessee State University. His most recent National Football League (NFL) experience was as the defensive coordinator for the New York Jets, from 2019 to 2020. Previously, he was head coach of the Buffalo Bills from 2001 to 2003, and defensive coordinator of the New Orleans Saints (with whom he won Super Bowl XLIV) from 2009 to 2011, and the Cleveland Browns, acting as an interim head coach in the 2018 season. Williams is known for running aggressive, attacking 4–3 schemes that put heavy pressure on opposing quarterbacks and for his key role in the New Orleans Saints bounty scandal, also known as "Bountygate".

In March 2012, Williams was suspended indefinitely from the NFL as a result of his admitted involvement in the New Orleans Saints bounty scandal, under which bounties were paid for causing injuries that would take targeted players on opposing teams out of games. Williams' suspension was lifted a year later, and he returned to the NFL.

Williams was inducted into the Missouri Sports Hall of Fame in 2016. In 2004, Williams helped create a charity, the "Gregg Williams Foundation", that benefits the local schools and community in his hometown of Excelsior Springs, Missouri. The charity has contributed over $2,000,000 since 2004 to benefit the Excelsior Springs community.

After graduating from Excelsior Springs High School (MO) in 1976, Gregg Williams played quarterback at Northeast Missouri State University (now Truman State University) in Kirksville, Missouri. He started his coaching career as an assistant football coach at this alma mater, Excelsior Springs High School (MO). After being passed over for the head coaching job at Excelsior Springs High School in 1983, he was hired as head coach for the Class 5 Belton High School Pirate football team in Belton, Missouri. After coaching at Belton High School for four seasons, Williams was hired in 1988 as an assistant coach at the University of Houston under former Washington Redskins head coach, Jack Pardee.

In 1990, Williams became the Special Teams coach of the Houston Oilers under then defensive coordinator, Buddy Ryan. From 1994 to 1996, Williams was the linebackers coach for the Oilers. From 1997–2000, Williams was promoted to defensive coordinator of the now Tennessee Titans after the Oilers moved out of Houston. As the defensive coordinator, the Titans led the league in total defense and only gave up 191 points, the third fewest in the NFL since the league adopted the 16-game schedule in 1978. The defense also helped lead the Titans to Super Bowl XXXIV where they lost to the St. Louis Rams. Williams was involved in the theft of the Baltimore Ravens quarterback Trent Dilfer's playbook in 2000 during a regular-season game, who claimed years later that Williams had previously admitted to doing so. A similar instance occurred in the 1999 AFC Championship Game, according to the former defensive lineman Renaldo Wynn, who claimed that Williams had admitted to having the Jacksonville Jaguars' playbook. Williams pushed back on using it for any advantage, claiming that he has every team's playbook and collects them.

Williams joined the Buffalo Bills as head coach in 2001 along with new team President and general manager Tom Donahoe. After three seasons in which the team compiled records of 3–13, 8–8, and 6–10 under his leadership, Williams' contract was not renewed after the 2003 season.

After his release from Buffalo, Williams was at the top of several NFL teams' list for the position of defensive coordinator. Williams quickly signed with the Washington Redskins, the only team with which he interviewed, because Head Coach Joe Gibbs offered him total autonomy over his defensive players and defensive coaching staff.

In Washington, with Williams' aggressive defensive scheme, the Redskins' defense ranked third in the NFL in 2004 and ninth in 2005.