The ability to conduct an effective clinical and diagnostic interview is arguably one of the most valued skills among mental health professionals. It is during the interview that the clinician learns about the difficulties and challenges experienced by the client and begins to form the foundations of a healing professional therapeutic relationship. Although the metaphor is not a novel one, the job of the interviewer may be likened to that of a detective trying to collect data and organize clues to “solve the mystery,” in this example, clarifying the presenting problem and diagnosis of the client. The most important aspect of this detective metaphor is that effective interviewers (detectives) are served well by their natural curiosity (truly wanting to understand all aspects of the client’s experiences, no matter how painful or uncomfortable) and the thoughtfulness of their approach (being guided by strategies and principles for gathering important data while also forming a positive connection with the client). This chapter discusses some of the key factors that facilitate the interview process. We begin with discussions of the different settings in which interviews occur, confidentiality, common factors, and the basic skills used in interviews, followed by a description of the importance of understanding aspects of client diversity on the interview process.