Laser powder bed fusion (L-PBF) of metallic alloys results in the formation of solid metallic material with microstructure different from the conventional analogs. The differences are the result of high temperature of the molten pool, high cooling rates, steep temperature gradient, thermal cycling during manufacturing, and other factors. Since the microstructure affects the physical and mechanical properties of materials and influences the performance of L-PBF parts, microstructural analysis is critical. Understanding of the formation of microstructure, therefore, is necessary to predict the final properties of the material, and it creates a strong basis for the microstructure control and manufacturing of components with tailored properties. This chapter outlines the main principles of the formation of microstructure in the L-PBF process and presents some examples of microstructures of the most common L-PBF alloys.