Self-assembled III-V quantum dots attract intense research interest and effort due to their unique physical properties arising from the three-dimensional confinement of carriers and discrete density of states. Semiconductor III-V quantum-dot laser structures exhibit dramatically improved device performance in comparison with their quantum well counterparts, notably their ultra low threshold current density, less sensitivity to defects and outstanding thermal stability. Therefore, integrating a high-quality quantum-dot laser structure onto silicon-based platform could potentially constitute a hybrid technology for the realization of optical inter-chip communications. This book is devoted to the development of high-performance InAs/GaAs quantum-dot lasers directly grown on silicon substrates and germanium substrates for silicon photonics.