Modern advanced semiconductor lasers show complex spatio-temporal dynamics of the emitted optical fields. This book presents fundamental theories and simulations of the spatio-temporal dynamics and quantum fluctuations in semiconductor lasers. The dynamic interplay of light and matter is theoretically described by taking into account microscopic carrier dynamics, spatially dependent light-field propagation and the influence of spontaneous emission and noise. Microscopic simulations reveal the internal spatio-temporal dynamics of in-plane lasers, high-power amplifiers and vertical-cavity surface-emitting lasers. The theory developed here provides the basis for the interpretation of measured emission properties and may serve as a predictive guideline for the design of advanced semiconductor lasers.