This book concerns the nature of time and ordinary cases of persistence in Spinoza. The author argues for three major interpretive claims. First, that Spinoza is committed to an eternalist theory of time whereby all things (whether they seem to be past, present, or future) are equally real. Second, that a mode's conatus or essence is a self-maintaining activity (not an inertial force or disposition.) Third, that modes persist through time in Spinoza's metaphysics by having temporal parts (that is, different parts at different times.) If the author is correct, then a significant reinterpretation of Spinoza's modal metaphysics is required. The book also puts Spinoza into dialogue with some recent work in analytic metaphysics.