This chapter provides a guide to assessing individuals with functional gastrointestinal disorders (FGIDs) from a psychological perspective. It presents currently available questionnaires that can be utilized in FGIDs to assess multiple domains. Psychological interventions and psychotropic medications are effective treatments for FGIDs. Psychological assessment has a dual role: diagnosis and treatment planning, but often more importantly, therapeutic engagement and education about the role of psychological processes in FGIDs. While anxiety- and depression-related disorders are most commonly identified in FGID cohorts, clinicians also need to be aware of other differential diagnoses. As an aside, one diagnostic challenge is that the Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5) does not offer a fully integrated view of mind-body problems. The chapter provides a list of the most common questionnaires available for the assessment of non-specific and specific FGID symptoms, anxiety, depression, stress, illness perceptions and quality of life.