This study explored the combined influence of shear flow and nucleating agents on isotactic polypropylene (iPP) crystallisation. The study showed that oriented α-iPP crystals were not necessary to form β-iPP crystals, contrary to the accepted view that the surface of oriented α-iPP crystals provides nucleation sites for an α-iPP to β-iPP growth transition. Instead it was proposed that flow-induced mesomorphic point-like nuclei preferentially nucleates β-iPP. The combined effect of shear flow and nucleant was found to promote γ-iPP crystals. The surprising γ-iPP nucleation effect was explained by the high density of flow-induced and heterogeneous nuclei present at the start of crystallisation.