<p>Nucleation, which is the initial step of crystallization, critically governs the polymer crystallization behavior, influencing the crystallization temperature, kinetics, and morphology. However, the direct observation of the nucleation process in polymers remains elusive owing to spatial and temporal resolution limitations. This feature article summarizes the recent progress in understanding polymer nucleation within confined and interface-dominated environments, focusing on three representative systems: anodic aluminum oxide templates and nanocomposites containing nanoparticles or nanosheets. The interplay between finite size and interfacial effects has revealed some novel phenomena, such as homogeneous nucleation, surface nucleation, prefreezing, and supernucleation.</p>