The Winslow Foundation is a private foundation that funds primarily left-leaning nonprofit organizations, especially environmentalist groups. Wren Winslow Wirth, the wife of Democratic politician, longtime United Nations Foundation president, former U.S. Senator from Colorado, and Clinton administration State Department official Tim Wirth, heads the foundation. 
According to left-leaning philanthropic resource Inside Philanthropy, the Winslow Foundation “maintains a low public profile, does not have a website, and employs a small formal staff of just three people.” 
The Winslow Foundation principally supports left-progressive environmentalist groups. In 2018, it funded the League of Conservation Voters Education Fund, Sunrise Movement Education Fund, Sustainable Markets Foundation, Virginia Organizing, and WildEarth Guardians. It further gave $250,000 to Mothers Out Front, a left-progressive environmentalist group founded by Kelsey Wirth, Wren Winslow and Tim Wirth’s daughter and a member of the Winslow Foundation board. 
Wren Winslow Wirth is the president of the Winslow Foundation. Wren is married to Tim Wirth, a Democratic politician who served in the U.S. House of Representatives from 1975 until 1987 and the U.S. Senate from 1987 until 1993. Tim Wirth then held the position of Undersecretary of State for Democracy and Global Affairs during the Clinton administration. 
Kelsey Wirth, the daughter of Tim and Wren, is a vice president and trustee of the foundation. She holds an MBA from Stanford University and is the founder of Mothers Out Front, a left-leaning alliance of mothers and grandmothers who advocate for environmentalist policy including the socialist Green New Deal. Kelsey is also the co-founder of Align Technology, a company that provides alternative materials for orthodontics. 
Christopher Wirth, the son to Tim and Wren, is a vice president and trustee of the foundation. Tim is also the founder of Liberty Puzzles.