Modern advanced semiconductor lasers show complex spatio-temporal dynamics of the emitted light. The interaction of light and matter is determined by a variety of nonlinear and quantum-optical processes that occur on various time and length scales. The active medium directly couples the microscopic ultrafast processes of the charge carriers and interband dipoles with the spatio-temporal dynamics of the optical fields. The dynamic interplay of spontaneous and induced emission determines the amplification of ultrashort optical signals and the performance of high-power lasers. Realization of novel waveguide structures and external feedback allow control of laser emission. Quantum dot media provide novel customized gain media by directly harnessing quantum effects. 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. Computer simulations reveal the internal spatio-temporal dynamics of quantum well and quantum dot in-plane lasers, high-power amplifiers and vertical-cavity surface-emitting lasers. The theories and simulations provide the basis for the interpretation of measured emission properties and may serve as a predictive guideline for the design of advanced semiconductor lasers