Underpinning any successful psychological intervention involves a comprehensive assessment, diagnosis, and formulation. Groth-Marnat (2003) identiﬁ es that the early forms of the psychological assessment were primarily based on medical formats. However, over time the modern day methods of psychological assessment have appeared and can involve multiple theoretical approaches, including psychoanalytic, humanistic, behavioral, cognitive, and cognitive-behavioral. While the majority of clinicians use a semi-structured approach (i.e. having a standard set of basic questions and then allowing open ended, and follow-up questions, into particular areas of clinical focus), the development of diagnostic criteria [e.g. Diagnostic and Statistical Manual (American Psychiatric Association, American Psychiatric Association, DSM-5 Task Force 2013)] or the International Statistical Classiﬁ cation of Diseases and Related Health Problems (National Centre for Classiﬁ cation in Health 2010) and the need for standardized methods for research has led to the development of structural diagnostic approaches, such as the Mini-International Neuropsychiatric Interview (M.I.N.I.; Sheehan et al. 1998) and Structured Clinical Interview for DSM (SCID; First and Spitzer 2002). This Chapter will brieﬂ y review the key features of a psychological assessment, with an emphasis on inﬂ ammatory bowel disease (IBD)-speciﬁ c questions. The Chapter will then identify currently available questionnaires that can be utilized in an IBD cohort to assess multiple psychosocial domains (e.g. anxiety, depression, stress, disease activity, illness perceptions, and quality of life).