Foam extrusion is one of the three major foam processing technologies, which is widely being used to manufacture low-density simple two-dimensional foam products. This chapter discusses the foam extrusion of polylactide (PLA) and its compounds. Foam extrusion of linear and branched PLA, PLA-talc, PLA-nanosilica, and PLA-nanoclay compounds are discussed in presence of gas/supercritical CO2. The significance of CO2-induced and shear-induced crystallization, heterogeneously nucleated crystals around different additives and through branched structure, as well as isothermal melt crystallization during foam processing on PLA's extrusion foaming behavior is extensively discussed in this chapter. Furthermore, the effects of linearity and branching on crystallization and foaming ability of PLA are disclosed. The effect of various micro-/nanosized additives on the PLA crystallinity, and more comprehensively on PLA foaming behavior, is revealed.