The wide environmental differences that occurs in space and time has an important bearing on the performance of crop plants and hence on the plant breeding process. The interaction between genotypes and the environment modifies the expression of genes. This phenomenon, usually referred to as genotype-by-environnement (GE) interaction, reduces the correspondence between the observed phenotype and the underlying genotype. In recent times, efforts have been directed towards understanding GE interactions in terms of their effects on growth, development and productivity. The aim has been to desing testing strategies in which the behavior of a genotype over varying environments could be predicted with greater precision and at minimum cost and time. In this article, the effects of GE interactions on the expression of bean and liquor qualities are discussed in relation to their influence on the efficiency of selection and testing of improved varieties of Coffea arabica L. Results from a multi-location trial in Kenya involving 22 complex hybrid varieties and two check cultivars planted in five locations form the suject of this discussion