Michael S. Weiner (December 21, 1961 – November 21, 2013) was an executive director of the Major League Baseball Players Association. He assumed the role on June 22, 2009, replacing Donald Fehr, becoming only the fifth executive director of the union. Weiner joined the organization in September 1988 and had been general counsel since 2004.  He was born in Paterson, New Jersey.

With Weiner at the helm, the union signed an agreement in November 2011 for a five-year contract running until December 2016, which ensures 21 consecutive years of labor peace in Major League Baseball. The agreement allowed for blood testing for human growth hormone, introduced restraints on bonuses for amateur draft picks and international signings, and restored salary arbitration eligibility for part of a class of players that lost it in the 1980s.  Weiner received his undergraduate degree in political economy from Williams College in 1983. He graduated from Harvard Law School in 1986. From 1986 to 1988, Michael served as law clerk to the Hon. H. Lee Sarokin, then United States District Court Judge, in Newark, New Jersey.   Weiner was diagnosed with a brain tumor in August 2012, and died fifteen months later, on November 21, 2013. He was 51 years old. He was succeeded by his Deputy, Tony Clark, the 1st former Major League Baseball Player to lead the union.