 With the perspective afforded by the mass of posthumous writings published since the 1990s, it has become clear that Althusser was perennially concerned with important issues in metaphysics, epistemology, philosophy of science, historiography, hermeneutics, and political philosophy. However, it is also true that the primary medium Althusser employed for thinking through problems in these areas was Marxist philosophy. This is especially true of the period between 1961 and 1966 when the majority of his published and unpublished work concerned itself with how to read Marx, the definition of Marxist philosophy, and how to understand and apply Marxian concepts. In addition, if we are to take Althusser’s retrospective word for it, the pieces he published during this period were intended as political-theoretical acts, polemics meant to respond to contemporary opinions and policies and to shift the terms of these arguments as well as the actions which were their results. For these reasons, it is natural when discussing these texts to focus upon the contexts that engendered them and upon the positions within Marxist philosophy that Althusser stakes out by their means. Alternatively, as Althusser indicates in many of these pieces his debts to contemporaneous theorists and to philosophical predecessors such as Spinoza, there is the temptation to understand his thought as a combination of the insights contributed by these thinkers with Marxist philosophy. While each is a useful approach to understanding and explaining Althusser’s philosophy, when excessive attention is paid to one or another of them, one risks historicizing his contributions or suggesting that they are merely derivative. Seeking to avoid either result, even though the following discussion will note the context for Althusser’s work, its relation to Marxist philosophy, and the non-Marxist philosophical insights that contribute to its method and conclusions, this account will also suggest the uniqueness of his contributions to hermeneutics, metaphysics, epistemology, philosophy of science, historiography, and political philosophy.