AbstractInvestigation of the crystallography of the thin platelike polymer crystals precipitated from dilute solution has led to the concept of chain folding in polymer crystallization. This unexpected and unusual phenomenon has produced much speculation about both its origin and its implications concerning the morphology of the polymer crystals. The theories which have been proposed to account for the observed effects fall into two categories: (a) equilibrium theories; and (b) kinetic theories. At the moment the kinetic theories appear to be the more successful in explaining the observed morphology and behavior of the polymer crystals. Essentially it is proposed that the plate‐like habit of the crystals results from the formation of crystal uncleii from single polymer molecules followed by a growth process whose rate is controlled by nucleation of new crystal layers on existing completed crystal faces. Quantitative observations of crystal growth rates and of the influence of supercooling on the thickness of the crystals are consistent with the predictions of these theories.