Mark David Melancon (/məˈlænsən/ mə-LAN-sən; born March 28, 1985) is an American former professional baseball pitcher and current coach. He played in Major League Baseball (MLB) for the New York Yankees, Houston Astros, Boston Red Sox, Pittsburgh Pirates, Washington Nationals, San Francisco Giants, Atlanta Braves, San Diego Padres, and Arizona Diamondbacks. Melancon was drafted by the New York Yankees in the ninth round of the 2006 MLB draft. He made his MLB debut in 2009. He led the National League in saves in 2015, and won the Trevor Hoffman Award that year. Melancon was an MLB All-Star in 2013, 2015, 2016, and 2021.

Melancon was born in Wheat Ridge, Colorado, and attended Golden High School, where he lettered all four years in baseball, basketball and three times in football. He was also named to several All-State teams in these three sports and helped win a Baseball State Championship in 2003. He was also a member of the National Honor Society.

Melancon was drafted by the Los Angeles Dodgers in the 30th round of the 2003 MLB draft. He declined the offer so that he could attend the University of Arizona.

As a member of the Arizona Wildcats baseball team, Melancon appeared in 29 games (a single-season freshman record) and played in 5 post-season games. He pitched in 10 games for the United States national baseball team that summer, and also played summer league baseball for the Duluth Huskies of the Northwoods League. In his sophomore year he worked as a closing pitcher, achieving 11 saves (a single-season record) in 34 appearances. He played a shortened season in 2006 due to a strained elbow ligament, and had a college career total of 18 saves.

The New York Yankees selected Melancon in the ninth round of the 2006 MLB draft. Melancon pitched for the Staten Island Yankees of the Class A-Short Season New York–Penn League in 2006. He missed the entire 2007 season after having Tommy John surgery in October 2006.

In 2008, he pitched for three of the Yankees minor league affiliates: the Single-A Tampa Yankees, Double-A Trenton Thunder and Triple-A Scranton/Wilkes-Barre Yankees, going 8–1 with a 2.27 ERA in 41 relief appearances, holding batters to a .202 batting average. Following the season, Baseball America rated him the organization's ninth best prospect.

Melancon was called up to MLB for the first time on April 25, 2009. He made his MLB debut as a relief pitcher against the Boston Red Sox on April 26, pitching two scoreless innings.

He was then optioned back to Triple-A team Scranton/Wilkes-Barre Yankees on May 8, and recalled back to the Majors on July 9.