Polymer crystallization often occurs in the presence of foreign bodies, such as fibers. If many nuclei are activated at their surfaces, their proximity imposes that entities emanating from these nuclei grow preferentially normal to the surface, leading to transcrystalline zones. This presentation will address three topics. 1. The competition between surface and bulk nucleation can be studied through crystallizations of thin polymer films in contact with pan surfaces in a DSC apparatus. A specific analysis of these DSC experiments makes it possible to measure the crystal growth rate and to determine the intrinsic crystallisation kinetics, i.e., not disturbed by transcrystallinity. 2. Another route to study both confinement and transcrystallinity effects is modelling. A general formulation of the overall kinetics equations has been applied to crystallization in a limited volume, without and with transcrystallinity at the surfaces. An example of this approach is to predict crystallization in thermoplastic fibrous composites. 3. Finally, studying transcrystallinity is a convenient way to evaluate the nucleating activity of fillers: graphene, natural fibers (cotton, flax, miscanthus, …) and even maize tissues. In the latter case, slight modifications of matrix growth rate have been also observed.