This course surveys techniques for modeling semiconductor lasers. It begins with a tutorial discussion of the physical mechanisms contributing to semiconductor laser gain. The theoretical framework which incorporates these mechanisms into a unified laser theory is outlined. Approximations (such as quasiequilibrium, free-carrier, rate equation, effective relaxation rate) and their validity will be elucidated. Also included is an overview of bandstructure calculation methods. The second part of this course addresses the implementation of the above theory (with and without approximations) to study specific laser systems, such as VCSELs, where detailed knowledge of the gain spectrum is useful for optimized design. The process of incorporating the theory into a computer code will be discussed. We will describe the treatment of bulk, quantum well and quantum dot structures and the differences in their optical properties. Also, we will show how the numerical model allows us to analyze experimental data and optimize laser performance in material systems ranging from near UV through the visible, and all the way to the infrared where many important telecommunication applications exist.