The crystallization behavior of polymers in nanocomposites with inorganic fillers (montmorillonite layered silicate, MMT) is reviewed. Various different polymers are comparatively discussed [poly(vinyl alcohol) (PVA), polypropylene (PP), syndiotactic-polystyrene (sPS), and poly(ethylene oxide) (PEO)] representing three types of filler/matrix interactions: strong specific interactions (PVA/MMT), weak/negligible interactions (sPS and PP/o-MMT), and “unfavorable” (PEO/MMT). In the case of PVA/MMT, crystallization of PVA is strongly promoted by MMT, also stabilizing a new crystal form not found in bulk PVA. For sPS and PP/o-MMT, crystallization is only moderately affected, exhibiting traces of simple heterogeneous nucleation and mostly bulk-like crystal structures, with very small traces on non-bulk crystals. For PEO, crystallization is impeded near the MMT surfaces, due to coordination of the surface cations to the PEO. In all cases smaller spherulite sizes develop when filler is added, independent of the size of the bulk polymer spherulites, whereas the crystallization temperature changes reflect the strength of the polymer/surface interactions.