Uniaxially oriented polypropylene (PP) is molten and crystallized isothermally from the oriented, quiescent melt. Nucleation and growth of differently oriented sets of crystallites (c set and a∗ set) appear to be decoupled. After shallow quench, crystallization is preceded by (spinodal) decomposition. Evolution is monitored by wide-angle X-ray scattering (WAXS) and compared with results of a SAXS study. Peak integrals (crystallinity) and minimum crystallite size are tracked. In the commercial starting material, a∗-set crystallites melt at 158 °C. The c set melts at 170 °C furnace temperature. After recrystallization, both sets melt at 170 °C. Isothermal crystallization is divided into two distinct phases. During nucleation, the crystallinity stays low. The second phase is dominated by crystallinity growth. At 150 °C, the c set is seeded first. At 145 and 140 °C a∗-oriented crystallites are the first. The first-seeded set starts to grow first. c-set crystallinity is always growing faster than a∗-set crystallinity. The evolution of the SAXS cross-diagram in the growth phase can be explained by both lamellae growing at right angles and block merging.