Causes and effects of nonlinearity in structures are surveyed and illustrated by means of examples. Geometrical and material nonlinearities, and nonlinearities due to bearings, friction, clearance, stops, etc., are described. Nonlinearity in stiffness is contrasted with nonlinearity in damping. Dynamic effects of nonlinearity, including jump phenomena, subharmonic resonance, and nonlinear coupling between modes, are illustrated. A discussion of criteria for smallness of motion to justify linearized treatment of nonlinear systems is given. Illustrative examples including vibration of flat plates, vibration of antenna mounts, and earthquake response of multi‐story buildings are described. A structural earthquake isolation system utilizing friction‐controlled foundation pads is presented. Analytical and numerical techniques for predicting the statistical response of the system are demonstrated. [Supported by NSF Grant GI‐34945. ]