This article attempts to understand the philosophical significance of Lenin's work, Materialism and Empiriocriticism (1909), by putting it in the historical perspective and context of the theoretical debates of the time. The author argues that Lenin's decision to engage in philosophical discussion was motivated by the need to respond to the growing struggles of Marxism, and specifically to the dangerous consequences of positivism that spread to Russia, which thereby led to a crisis in theory and political practice. Lenin's work is the first philosophical assault on positivism, and most notably on its specific form, Machism, which he criticizes from the position of dialectical materialism. Recognizing the damaging effects of the positivistic position for Marxism, Lenin attacks Alexander Bogdanov's Empiriomonism as a form of Machism which undermines the materialistic foundation of Marxist philosophy.