Jill Ellen Stein (born May 14, 1950) is an American physician and activist who was the Green Party's nominee for President of the United States in the 2012, 2016, and 2024 elections. She was the Green-Rainbow Party's candidate for governor of Massachusetts in 2002 and 2010.

During her time as a practicing physician, she advocated for the improvement of air quality standards for coal plants. Stein ran her first political campaign running as the Green-Rainbow candidate for governor of Massachusetts in 2002, losing to Republican Mitt Romney. She ran for the same position again in 2010, this time losing to the then-incumbent Massachusetts governor, Democrat Deval Patrick.

Stein first ran for president of the United States in 2012 selecting Cheri Honkala as her running mate. They lost to the Democratic ticket of incumbent President Barack Obama and incumbent Vice President Joe Biden. She ran for the second time for president in 2016 with running mate Ajamu Baraka, against Democratic candidate Hillary Clinton and Republican candidate Donald Trump, the latter of whom won the election. In 2017, Stein was investigated by the Senate Intelligence Committee for possible collusion with the Russian government.