Introduction -- History of the fishery -- Tagging -- Movement of crabs -- Biology -- Summary -- Acknowledgments -- Literature cited. Results of studies beginning in 1947 on the biology of the Dungeness crab (Cancer magister) in Oregon coastal waters are reported. A review is made of the history of the fishery with regard to trend of the catch by magnitude, area, and season; the development and conduct of the fishery itself; and the regulations governing the fishery. The first reported commercial crab landings in Oregon were 6,628 pounds in 1880. The fishery expanded slowly until 1933 after which the catch rose sharply to a peak of about 11 million pounds in 1943. Landings in recent years have fluctuated between 6 and 11 million pounds from a commercial fishery which is carried out along the major portion of the Oregon coast. During the period 1947-50, 6,249 tagged crabs were released in offshore and bay waters of Oregon and 34.6 percent of the tags were subsequently recovered. The average movement of 1,042 recoveries of crabs released in offshore waters, as measured by the distance from the tagging site, was 8.3 miles (range 0-133 miles) in 80 days. For crabs released within bays, 606 recoveries averaged a minimum distance traveled of 4.2 miles (range 0-81 miles). Fifty-seven percent of the recoveries of offshore releases and 84 percent of the recoveries of bay releases were made within 4 miles of the respective tagging sites. Over 90 percent of the recoveries of offshore releases were made within 6 months, although 3 crabs were out more than a year with 1 at liberty 878 days. Tagged crabs moved from offshore to bays, from bay to bay, and from bays to offshore. There was no significant difference in percentage recovery for crabs with or without missing appendages. Egg-bearing female crabs are present in offshore waters during the period October to March, inclusive. Larval crabs assumed to be C. magister were observed in offshore waters from April to July, inclusive. Considerable variation in early growth of post larval crabs was observed in laboratory experiments. The amount of growth of crabs between 6.4 and 146.0 mm., as observed by measuring them before and after molting, increases until a shoulder width of about 95 mm. is reached. The increase with each subsequent molt thereafter remains relatively constant. Macroplankton-eating fishes feed upon free swimming crab larvae. Adult crabs up to at least 114 mm. in shoulder width are preyed upon by voracious fish such as ling-cod (Ophiodon elongatus), the great marbeled sculpin (Scorpaenichthys armoratus), wolf eel (Anarrhichthys ocellatus), halibut (Hippoglossus stenolepis), and some of the rock fishes of the genus Sebastodes.