Polymeric nanomaterials offer broad applicability in drug delivery, biomedicine, and functional materials due to their tunable size, morphology, and surface properties. However, achieving true uniformity — consistent size in all three dimensions, uniform morphology, and ordered internal packing — remains a central challenge. This review focuses on bottom‑up strategies for constructing uniform polymeric nanomaterials, with particular emphasis on crystallization‑driven self‑assembly (CDSA). While living CDSA enables exceptional control over nanostructure length and lateral area along epitaxial growth directions (a/b axes), the independent regulation of dimensions in the non‑growth direction (c‑axis) — i.e., the diameter of 1D fibers and the thickness of 2D platelets — remains largely unmet due to the complexity of polymer chain folding. Unlike previous reviews that focus primarily on CDSA’s morphological control, this review places the non‑growth direction at the center of the design paradigm. We analyze why c‑axis control is fundamentally harder, survey emerging molecular strategies, and present our own complementary approaches — controlled main‑chain folding via precision defects and side‑chain extended crystallization — that enable programmable thickness control. This review provides a mechanism‑oriented framework for the precise, full‑dimensional construction of uniform polymeric nanomaterials.