This thesis presents the fundamental and experimental investigation of cell nucleation and growth mechanisms in advanced Micro-/Nano-Layered (MNL) polymeric structures with alternating film and foam layers. Novel strategies to optimize MNL structures are also developed. It is found that the final cell morphologies in MNL systems are governed by the synergy of two categories of parameters:​ morphological parameters, i.e., layer thicknesses and interface densities;​ and material parameters, i.e., material stiffness and material compatibility. The presence of adjacent film layers can significantly increase cell densities and decrease cell sizes through two mechanisms:​ promoting heterogeneous cell nucleation and preventing cell deterioration. Stiffer and more compatible film layers produced higher cell densities by further boosting these two mechanisms. Moreover, as a stiffness-enhancing strategy, the crystallization of PC layers was successfully achieved for the first time in MNL structures, resulting in more pronounced optimizations in cell morphologies.