For the transition toward a circular economy, it is essential that products are returned for reuse, refurbishing or recycling. In order to address the lack of literature on the topic from a user perspective, this paper explores how users can be stimulated to return used smartphones. Taking a Research through Design approach, we developed a novel set of "design for divestment" principles. Divestment is the process users experience when separating from a product. After introducing a conceptual model of divestment based on an extension of the Consumer Decision Process model by Blackwell, Engel, and Miniard, we describe seven empirical studies (i.e., design projects) into smartphone divestment. The studies explore factors that influence a successful divestment process. We report on a highly complex process with interrelated factors changing over time. While it is impossible to define a blueprint for an ideal divestment process, several patterns emerged such as the need to emotionally support users, to give them confidence regarding data security, and to provide information at the right moment. These unique insights contribute to consumer research (i.e., circular consumption); and by translating the insights to ten design principles for divestment, a novel contribution is made to the field of design research.