Lenni Brenner (born 1937), formerly known as Leonard Glaser or Lenny Glaser, is an American Trotskyist writer. In the 1960s, Brenner was a prominent civil rights movement activist and vocal opponent of the Vietnam War. Since the 1980s, his activism has focused on anti-Zionism. He has published widely on the history of Zionism, in particular asserting that the movement collaborated with the Nazis.