The expression and heritability of quantitative traits were examined in four hybrid mungbean populations, developed by crossing two cultivars, Kiloga and Berken, with two Australian wild accessions, ACC 1 and ACC 87. Phenological, morphological, agronomic and pod and seed traits were measured in the parental, F₁, F₂, and two F₁ × parent backcross progeny generations. Plants were grown in large pots on benches, in autumn in the field at Townsville, Australia. The two cultivars were both early flowering (∼5 weeks) and short duration, with short, thick stems, few branches, large leaflets, pods and seeds, and high harvest index. There were greater differences between the two wild accessions. ACC 1 was very late flowering (>12 weeks) even under the short days of autumn, and strongly indeterminate, with prostrate habit, prolific branching, thin stems, small leaflets and tiny seeds. The perennial type ACC 87 was intermediate in flowering (∼6 weeks), with more robust, albeit still branched and twining growth habit, and larger leaflets, flowers, pods and seeds. Flowering in all crosses was conditioned by additive gene action with some dominance effects (with lateness recessive to earliness). The responses suggested that the extreme lateness of ACC 1 was due to the cumulative additive effects of multiple lateness genes. For most other traits, there were broad consistencies in trait expression in hybrid progeny and heritability between the different crosses, indicating general similarities in genetic control. Although broad-sense heritability for most traits was high, narrow-sense heritability was high to very high for twice as many traits in the ACC 87 as in the ACC 1 crosses, indicating higher levels dominance effects in the latter crosses. Several genetic and phenotypic correlations were identified between various traits, as well as associations between quantitative traits in this study and previously reported qualitative traits from the same populations. There were no gross genetic incompatibilities between the wild and cultivated accessions. However, irregularities in the segregation patterns in the progeny generations for seeds per pod suggested that there may have been cryptic hybrid breakdown effects at the gametic or zygotic level. The results of this study indicated that ACC 1 and ACC 87 are genetically distinctive, with the perennial form ACC 87 actually less distant from the domesticated mungbean than is ACC 1. The research provides yet further evidence that the Australian wild accessions add significant diversity to the mungbean primary germplasm.