Chaos and complexity are related concepts that help explain patterns in nature, and the inherent limitations we face in trying to interpret them. This chapter is a relatively straightforward examination of these two fields, but it applies them specifically to the biological sciences, demonstrating the constraints on prediction and inference in biological systems, especially evolutionary systems, based on chaos theory. Complexity theory explains how nature can create complex functioning systems, whether they are anatomical or behavioral, and reveals how we can get something as complex as the eye, or consciousness, as an emergent property of a complex system following simple biological or physical rules. The ways in which emergent properties can be contrasted to engineered solutions are emphasized.