||What is it for an object to persist over an interval of time? How is persistence achieved? Do objects exist through changes in their intrinsic properties or do such changes cause the object to go out of existence only to be replaced by another more or less similar object? The theory of persistence tries to give principled answers to the these questions, drawing on theoretical physics, philosophical intuition and argumentation, and careful reflection on the phenomenology of objects. The most popular answers to these questions are represented by a pair of competing theories: endurantism, the view according to which objects endure, or "sweep," through time taking all their three-dimensional parts with them; and perdurantism, the view according to which objects are composites or "worms" of temporal parts existing in a four-dimensional spacetime manifold. A third important theory is the "stage" theory favored by some perdurantists, on this view objects are, strictly speaking, identical with momentary temporal parts or "stages" in a four-dimensional spacetime manifold and to say they persist is merely a facon de parle.