An outline of a comprehensive breeding system developed and used by the Kenya Maize Research Section is presented. This system has four main phases: 1. Evaluation of local and exotic varieties so that the breeding material is the best available. 2. Compositing the selected breeding material into two or more populations or varieties in such a manner that each population has considerable genetic variation for the traits requiring improvement and that the crosses of these populations will show heterosis. 3. Recurrent selection in each population to increase the frequency of favorable genes so that the populations and population crosses are improved with each cycle of selection. 4. Release of a commercial variety of one of the following forms: (a) the cross of two populations as a variety cross hybrid; (b) single, three-way or double cross hybrids from inbred lines developed from the elite material after each cycle of selection; or (c) a synthetic variety derived from the advanced generation of the population cross in areas where hybrid production is not yet feasible.