Jill Ellen Stein is an American physician, activist, and politician. She was the Green Party nominee for President of the United States in the 2016 election.

As a medical doctor, Stein became increasingly concerned about the connection between people's health and the quality of their local environment and decided to turn her focus to activism in 1998.

She has served on the Greater Boston board of Physicians for Social Responsibility. Stein co-founded and served as Executive Director of the Massachusetts Coalition for Healthy Communities. She has worked with include Clean Water Action, Toxic Action Center, Global Climate Convergence, Physicians for a National Health Program, and Massachusetts Medical Society.

Stein is also an advocate for campaign finance reform. In 1998, she helped campaign for the Clean Elections Law in Massachusetts. She has also served on the board of MassVoters for Fair Elections and has campaigned for implementing instant runoff voting in Massachusetts.