Foam injection molding is also one of the major foam processing technologies, which is widely being used to manufacture continuous high-density complex three-dimensional foam products. This chapter discusses the foam injection molding of polylactide (PLA) and its compounds. Foam injection molding of linear and branched PLA with chemical blowing agent and PLA-talc and PLA-nanoclay composites/nanocomposites with supercritical physical blowing agent are discussed in the presence of dissolved N-2 and CO2. The significance of gas-induced and shear-induced crystallization, heterogeneously nucleated crystals around different additives and through branched structure, as well as isothermal melt crystallization is extensively discussed in this chapter. The achievement of microcellular PLA foams with void fractions as high as 55% is discussed via using low-pressure and high-pressure foam injection molding as well as gas counterpressure and mold opening foam injection molding techniques using chemical and physical blowing agents.