Abstract: Epistasis was thought to be absent in the inheritance of most of the traits of economic worth such as yield, but there is growing enthusiasm and evidence that it is an integral part of genetic architecture of quantitative traits. Epistasis, when present, causes bias in the estimation of important genetic parameters resulting in erroneous estimates of expected gain under selection. This hampers the efficiency of breeding programmes aimed at exploitation of various components of genetic variance such as additive and dominance. The effect of epistasis on genetic variance components is all the more important in view of the fact that none of the mating designs developed so far ensures that epistasis if present does not influence the estimates of genetic components. A number of studies in maize have established the fact that epistasis has a significant role in trait expression but, as of now, all the genetic models to test and estimate it precisely are elusive. Recent studies with molecular markers have clearly revealed that epistasis has a significant role in inheritance of quantitative traits as well as plant growth and development. It would thus be logical to search for epistasis and optimize its use in the development of promising cultivars for target environments rather than attributing it to left over variance after additive and dominance effects are accounted for.