The goal of my research program is to employ biochemical and molecular techniques to gain ecological insight into the role of temperature in setting species' distribution patterns in the marine environment. Our central focus is the study of the environmental regulation of gene expression, where we are particularly interested in a set of inducible molecular chaperones, the heat-shock proteins (Hsps), and how the expression of these genes varies with the thermal history of organisms in natural populations. The primary study organisms are intertidal invertebrates and marine fish that experience dramatic changes in body temperature on varying temporal and spatial scales. In this review, I present studies that address the variable expression of Hsps, how these genes are differentially regulated in ectothermic animals in response to ecologically relevant temperature conditions, and how such plasticity in gene expression contributes to physiological plasticity in the environment.