<p>There is longstanding interpretive dispute between commentators over Spinoza’s commitment to <i>necessitarianism</i>, the doctrine that all things are metaphysically necessary and none are contingent. Those who affirm Spinoza’s commitment to the doctrine adhere to <i>the necessitarian interpretation</i> whereas those who deny it adhere to what I call <i>the semi-necessitarian interpretation</i>. As things stand, the disagreement between commentators appears to have reached an impasse. Notwithstanding, there seems to be no disagreement among commentators on the question of necessitarianism’s philosophical plausibility as a metaphysical view: the doctrine is wildly untenable. This consensus view is more relevant to the interpretive debate than few have recognized, since leading semi-necessitarian commentators take the doctrine’s alleged absurdity to be one of the most compelling reasons (if not <i>the</i> most compelling reason) to prefer their reading over the necessitarian interpretation: for, as a matter of methodological principle, great philosophers like Spinoza should not be ascribed ridiculous views in the absence of better evidence. </p> <p>This dissertation seeks to defend Spinoza’s commitment to necessitarianism on both the interpretive and philosophical fronts. I argue not only that the necessitarian interpretation of Spinoza is more plausible than the semi-necessitarian interpretation on textual grounds, but that Spinoza’s necessitarianism is a serviceable philosophical view whose tenability has been almost entirely overlooked and perfunctorily rejected. The principal basis upon which I build this defense is Spinoza’s rich and fascinating view of essences—what I simply refer to as his <i>essentialism</i>. Spinoza’s essentialism forms the bedrock of his metaphysics and is significant not least because it underlies and informs doctrines like his necessitarianism. Spinoza’s essentialism supplies resources to answer not just interpretive problems associated with necessitarianism, but philosophical challenges to the plausibility of the doctrine. My defense of Spinoza’s necessitarianism on philosophical grounds also offers a novel way of getting past much of the current interpretive impasse among commentators by effectively undercutting the methodological motivation for the semi-necessitarian reading. In addition to my defense on the interpretive front, then, my defense on the philosophical front provides supplementary reason to <i>a fortiori</i> favor the necessitarian reading of Spinoza.</p>