Polymers and polymer‐based composites are increasingly displacing more traditional materials in a wide variety of engineering applications, and as such characterization of their fatigue behavior is of utmost importance. This article presents a general overview of the fatigue behavior of polymers. After a brief introduction that includes general terminology, the effects of test conditions (sample geometry, loading frequency, etc) are discussed. The effects of these conditions are also discussed in relevance to both the high cycle and low cycle fatigue behavior. Current models for predicting fatigue life are also reviewed, including cumulative damage theories and fatigue crack propagation models. Morphological and environmental effects are then discussed over a broad range of semicrystalline, amorphous, and modified polymer systems.