A central aim of ecology is to elucidate how species ranges are established and maintained. The biogeographic ranges of marine coastal species are often quite extensive encompassing a great deal of environmental variation. Whether this variation is detrimental physiologically and acts to limit species ranges is not well understood. In this dissertation, gene expression of the purple sea urchin, Strongylocentrotus purpuratus, was assayed across its entire coastal biogeographic range from Baja California to southeast Alaska. Measuring a physiological metric, e.g. gene expression, across a species' range under natural environmental conditions is a novel step toward understanding how environmental variation directly affects the physiology of a species. Specifically, tubefoot tissue samples were removed from S. purpuratus individuals across its range from Oregon to Baja California, Mexico and flash frozen in the field in order to preserve their natural physiological states. Gene expression of these samples was assayed in three experiments using either real-time quantitative PCR (qPCR) or a custom cDNA microarray on the total RNA isolated from the tissue samples. First, a qPCR comparison between S. purpuratus from central Oregon and from the Santa Barbara Channel, California revealed regulatory differences in the thermally sensitive gene, heat shock protein 70 (hsp70). Tissues from the Santa Barbara S. purpuratus displayed maximum transcription of hsp70 at 26°C, while transcription in the tissues of S. purpuratus acclimatized to the colder waters of Oregon began decline at temperatures above 23°C. Second, qPCR of six candidate genes showed that variation in expression may be as pronounced at meso-scales (< 50 km) as it is at larger scales (> 500 km). Finally, cDNA microarray analysis showed that the transcriptome of S. purpuratus in Oregon, within the northern region of their range, was most similar to those in Baja California, near their southern range edge. Overall, transcriptional variation in S. purpuratus was as pronounced at smaller spatial scales than across its entire biogeographic range. This result suggests that the environment at Strongylocentrotus purpuratus' southern range edge may be no more physiologically challenging than those encountered across the remainder its range.