In recent years, metal additive manufacturing (AM) has receivedincreasing interest in the field of manufacturing engineeringbecause of its attractive features compared with those ofconventional manufacturing methods. Due to the inherentnature of this process, complex thermal conditions drive phasetransformation from liquid to solid as well as phasetransformation in the solid state. A deeper and betterunderstanding of the relationships between the complex thermalconditions and the microstructure formation is vital for fullyutilizing the full potential of the AM processes. Achieving thisgoal with only an experimental approach is costly, timeconsuming, and in some cases, impractical. Consequently,computational modeling and simulation techniques areimportant complementary methods that help to achieve thisgoal. Different models are used to model different aspects of themicrostructure. The primary intention of this chapter is to givethe reader an overarching view (including a basic understanding of the formulation, limitations, applications, and challenges) ofcommonly used microstructure modeling and simulationtechniques in the context of the metal powder AM process.