This report describes the social organization of bobcats (Lynx rufus) during a 3-year study of their ecology in southeastern Idaho. Most information was based on 103 captures of 66 bobcats and 531 daily radiolocations of 17 bobcats wearing radio collars. Size of home ranges varied from 6.5 to 107.9 km2. Females appeared to use their smaller ranges more intensively than did males. The movements of all bobcats were more restricted during the autumn-winter than spring-summer periods. Resident females had almost exclusive ranges, but male ranges overlapped each other as well as female ranges. Only a small proportion of range overlap areas were mutually shared, and then primarily during periods of environmental hardship. Land tenure was apparently based on prior rights as few adult social interactions were observed. Various scent marks were made by bobcats to advertise their