A content item uploaded to a content management system from a client device can be assigned to one of multiple user accounts on which the client device is authorized. The user account can be selected based on account selection rules dictating selection of a user account based on various factors. For example, the account selection rules can dictate selection of a user account based on the type of user account; the type of content item; the client device that created the content item; the time the content item was created, modified, or uploaded; the location the content item was created, modified, or uploaded; etc. The account selection rules can be specified by a user or be heuristics based on general assumptions, data gathered regarding the user, and/or historical data gathered from content items already assigned to the user accounts. The content item can be assigned to the selected user account.