The rocky islands and rugged habitats of the outer Oregon coast and the low flat islands of the Columbia River estuary provide habitat for approximately 1.3 million nesting seabirds representing 15 species. Current and historical information on colony locations and estimates of breeding seabirds were compiled into databases, for all known seabird colonies in Oregon. A total of 393 colonies were identified, and maps and data tables for each colony are presented in this catalog. Specific information regarding date, observers, type of survey, quality of the estimate, and source of the data are provided for each record. The geographic scope of this catalog encompasses seabird colonies in marine and estuarine environments. The waters off the Oregon coast are part of the California Current System, one of the most productive marine habitats in the world. The rugged coast encompasses large expanses of rocky shorelines, islands, and offshore sea stacks, which provide nesting habitat for seabirds. This Catalog of Oregon Seabird Colonies presents a detailed record of seabird nesting sites along the Oregon coast. For each of the 393 sites identified in this catalog, the location, species composition, and abundance of breeding birds are presented. Survey data from 1901 to 2004 are included. Approximately 1.3 million seabirds, representing 15 species, nest in the state (Table 1, Figure 1). This represents approximately half of the seabirds breeding along the west coast of the conterminous United States, including two species (scientific names are in Table 1) of storm-petrels (Leach's and Forktailed), three species of cormorants (Double-crested, Brandt's, and Pelagic), three species of gulls (Western, Glaucous-winged, and Ring-billed), one tern species (Caspian), and six species of alcids (Common Murre, Pigeon Guillemot, Marbled Murrelet, Cassin's Auklet, Rhinoceros Auklet, and Tufted Puffin). One shorebird species (Black Oystercatcher) is also included because of its strong affiliation with marine habitats and the high degree of overlap between seabird and Black Oystercatcher nesting sites. This catalog it restricted to seabird species that breed along the coast and in the lower estuaries within Oregon state boundaries. Along the Pacific coast, seabird colony catalogs have been published for Alaska (Sowls et al. 1978), California (Sowls et al. 1980), and Washington (Speich and Wahl 1989). Similar catalogs of colonies in British Columbia, Canada have also been published (Drent and Guiguet 1961, Campbell et al. 1990). The first comprehensive survey of Oregon seabird colonies was conducted in 1979 (Varoujean and Pitman 1980) and a draft catalog was prepared (Pitman et al. 1985), but never published. Another complete survey of Oregon colonies was conducted in 1988. In addition to these comprehensive surveys, numerous other surveys of specific species at specific colonies have been completed, including, since 1988, annual aerial photographic surveys of Brandt's and Double-crested cormorants and Common Murres (all colonies have been photographed annually and a subsample of the colonies have been counted; see Methods), and a coast-wide survey of cormorant colonies in 2003. This catalog provides a compilation of current and historic seabird colony information. This catalog was designed primarily to provide biologists, resource managers, regulatory agencies, and researchers with the best available data on the size and location of Oregon seabird colonies, in a standardized format. The information compiled here serves as a baseline of recent and historic distribution and abundance of breeding seabirds in the state. In the event of an oil spill or other catastrophic occurrence, this catalog can provide quick reference to concentrations of breeding seabirds. The catalog will also be useful to community planners and members of the general public interested in increasing their understanding of Oregon's diverse seabird community.