I conducted a literature review of Harbor Seal dietary composition within the northern California Current Large Marine Ecosystem (CCLME). Papers examining quantitative dietary information from stomach contents and fecal hard-part analyses were used to create a comprehensive list of Harbor Seal prey in the northern California Current System. The study regions included Washington, Oregon, and the Columbia River, and were divided by Harbor Seal stock. Fourteen papers from the years 1931 to 2013 were compiled to obtain a comprehensive and quantitative evaluation of Harbor Seal dietary composition. Harbor Seals consumed a seasonally and spatially-varied diet, including fish, invertebrates, mammals, and birds of 120 species or genera from 37 taxonomic orders and 62 families. The Hood Canal, Oregon-Washington Coastal, and Southern Puget Sound Stocks of Harbor Seals were well-represented. Salmonids were detected in 13.3% of samples collected in Oregon, 27.8% in Washington, and 23.74% of samples overall. The large variety of prey species and regional differences are reflective of opportunistic foraging behavior in Harbor Seals. This paper summarizes findings for this comprehensive assessment of Harbor Seal dietary composition in the northern CCLME.