The behavior of nonliving and living systems is generally viewed as being qualitatively different. The key difference is often summarized by saying that whereas living systems are complex, nonliving ones are simple. This distinction is often the basis for claiming essential differences in conceptual stances, methods, and theories between scientific fields. I argue first that nonliving systems can display the unpredictable, irreducible, irreversible, and emergent-in sum, complex-properties of living systems. Then I discuss an emerging field called complexity theory, the principles of which offer the promise of bringing quantitative unity to an enormous range of phenomena, living or dead.