Heterotic group theory is one of the fundamental concepts which allow the maximum exploitation of the available genetic diversity in maize. The development of potential heterotic groups and identification of their subsequent heterotic patterns has been proved to be a crucial factor in hybrid maize breeding. Dissecting the genetic basis of a specific heterotic pattern is also useful in devising possible breeding strategies for the utilization of elite inbred lines in the breeding program. Genetic diversification of the available genetic pools is a key to develop genetically divergent heterotic groups which results into the development of superior heterotic patterns in maize. Estimation of combini ng ability (SCA and GCA) effects supplemented with pedigree information, phenotypic clustering and molecular marker characterization has been predominantly utilized to develop hete rotic groups in maize. The present review will focus on (i) to explain the b asic concept of heterotic group theory along with its evolution and advancements in accordance to hybrid maize breeding. (ii) Underpinning the genetic basis of heterosis in maize. (iii) Review different hetero tic group classification strategies along with their relative efficiencies and their combined application through a proposed conceptual framework. (iv) A comprehensive review about different heterotic groups developed in maize up till now and (v) future directions for the improvement of heterotic group concept in maize.
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