This chapter offers an introduction to understanding and working with people who have dissociative self-states (DSS). Toward this end, the chapter discusses similarities and differences between DSS and normative self-state functioning, the link between DSS and disorganized attachment, descriptions of DSS systems, relationships between DSS, and functions of DSS. The chapter then offers principles for working with persons with DSS and describes commonly encountered DSS types and strategies for working with them. In addition, this chapter includes examples of ways to respond to and work with patients presenting with specific, common challenges, such as working with self-states in relation to unsafe or risky behaviors; investigating the underlying concerns of patients who have self-states reluctant to make changes in their thinking and/or behavior; working with patients who cannot remember their behavior, experiences, or a previous session; and working with childlike self-states.