Abba Ahimeir (Hebrew: אב"א אחימאיר‎, 2 November 1897 - 6 June 1962) was a Russian-born Jewish journalist, historian and political activist. One of the ideologues of Revisionist Zionism, he was the founder of the Revisionist Maximalist faction of the Zionist Revisionist Movement (ZRM) and of the clandestine Brit HaBirionim.

Abba Shaul Geisinovich (later Abba Ahimeir) was born in Dolgi, a village near Babruysk in the Russian Empire (today in Belarus). From 1912-1914, he attended the Herzliya Gymnasium high school in Tel Aviv. While with his family in Babruysk for summer vacation in 1914, World War I broke out and he was forced to complete his studies in Russia. In 1917, he participated in the Russian Zionist Conference in Petrograd and underwent agricultural training as part of Joseph Trumpeldor’s HeHalutz movement in Batum, Caucasia to prepare him for a life as a pioneer in the Land of Israel. In 1920, he left Russia and changed his name from Gaisinovich to Ahimeir (in Hebrew: Meir’s brother) in memory of his brother Meir who had fallen in battle that year fighting against Poles during a pogrom.