Introduction.- The Wiggler Field And Electron Dynamics.- Incoherent Undulator Radiation.- Coherent Undulator Radiation.- Stimulated Emission: Linear Theory.- Nonlinear Theory: Steady-State Analysis.- Nonlinear Theory: Time-Dependent Analysis.- Sideband Instabilities.- Wiggler Imperfections.- Coherent Harmonic Generation.- Oscillator Theory.- Oscillator Simulation.- Self-Amplified Spontaneous Emission.- Segmented Wiggler Configurations.- Optical Klystrons And High-Gain Harmonic Generation.- Electromagnetic-Wave Wigglers.- Chaos In Free-Electron Lasers.