Phenotypic plasticity is the capacity of genes to respond to environmental variation, the outcome of which is the production of alternative phenotypes under differing environmental conditions. Plasticity can be adaptive, leading to the expression of selectively advantageous phenotypes under divergent conditions- potentially buffering populations from evolutionary change. Alternatively, plasticity can result in disadvantageous, or in some cases, novel phenotypes that can influence the subsequent course of evolution. A core area of research in our laboratory involves the interface between selection, plasticity and contemporary evolution. Our research in this area focuses upon behavior, life history and, in collaboration with Matthew Wund, morphological evolution, each of which tends to display differing but variable levels of plasticity. We are extending this research to include plasticity of gene expression and its role in evolutionary transitions via expression of underlying cryptic genetic variation. This new research direction involves the expression of salinity tolerance and its evolution in collaboration with Kevin Laland, William Cresko, John Gibbons and Juha Merilä. The adaptive radiation of the threespine stickleback offers an unparalleled opportunity to evaluate the role of ancestral plasticity in subsequent evolution for the reasons described below.