Numerous laser diode (LD) models can be found in literature and available as commercial design tools from several software developing companies. These models vary quite significantly in terms of the computational resources required, complexity, and accuracy. This fact is a consequence of a large variety of problems that are related to the LD modelling and design process. Hence, the selection of an appropriate model depends on many factors like, for instance, the type of LD, that is, vertical cavity surface emitting laser (VCSEL) diode or edge emitting laser diode (EELD). Furthermore, a LD can operate either as a stand-alone device or within an external cavity scheme. The type of the resonator is also an important factor, for example, Fabry-Perot, distributed feedback (DFB), or distributed Bragg reflectors (DBR) LD resonators. Considering the operating conditions, a LD can operate in a continuous wave (CW), in directly modulated (by current injection), pulsed, or self-pulsed mode (e.g. passive mode locking). Additionally, a design engineer may be focused only on a particular LD operating region of the L-I-V characteristics, for example, a near threshold behaviour, moderate output power operation, or a high output power operation. Finally, the choice of the appropriate model is influenced by the imposed set of target design parameters, for example, wall-plug efficiency, threshold current, and vertical and horizontal beam divergence.