This chapter is an integration of clinical approaches of two authors, Andrew Seubert and Robin Shapiro. It begins with a neurologic and functional explanation of the origin of ego states or “parts.” A brief description of the history of various models of ego state therapy is presented, and is followed by a description of the common elements among them, represented in the acronym RUG-C (recognition, understanding, gratitude/goals, collaboration). Work with parts is described during the evaluation and preparation phases of treatment, with special attention given to attachment injury and attachment repair. Several ways of processing (i.e., metabolizing, painful memories, and how to integrate these changes into the larger context of the client’s life) bring the chapter to a close.