In much of the world, the socialist left is fragmented, divided, and weak. The need for a united socialist movement that can defeat the billionaires and the far right is obvious. However, divisions of the left can reflect real and genuine differences over political principles, strategies, and tactics. The influence of social democracy, Stalinism, and liberalism still corrupts large portions of the socialist left. This talk will explore how revolutionaries can struggle to build a united socialist left without watering down on clear Marxist politics.