This book will offer a full reconstruction of the history of Theoretical Marxism in Italy between 1895 and 1935, based on a rigorous philological method. The starting term (1895) is marked by the publication of Antonio Labriola's first essay on historical materialism (In memory of Communist Manifesto); the final term coincides with the conclusion of the "e;Prison Notebooks"e; written by Antonio Gramsci. This book analyses the original character of the Marxist philosophy in Italy, which emerged by distinguishing itself from the "e;orthodoxy"e; of the Second and Third International. By delineating a significant chapter in the history of Marxism, the book will also propose a specific contribution to the history of Italian Philosophy, which is here studied in relation to the developments of European philosophy, beyond the traditional subdivisions of Positivism, Idealism and Marxism.