The purpose of this paper will be to review experimental results relating to choice of breeds. Considerable research has been conducted and much is in progress in the United States, primarily as a result of beef cattle breeding regional projects (W-1, NC-1 and S-10). The parameters of primary importance in choice of breeds are breeding values determined by average gene effects for the breeds and heterosis effects determined by interaction of gene effects and differences in average gene frequency between breeds (Willham, 1969).