Patient presentations are deemed complex due to a variety of factors, including the presence of multimorbidity, polypharmacy, and biopsychosocial elements that implicate their care. Identifying which patients are complex would improve management of their care and help prevent complications leading to lowered quality of life. The role of the pharmacist in complex patient cases is essential for optimizing healthcare delivery. Increasing pharmacist involvement in healthcare teams leads to improvement of patient health, evidenced by quantitative lab results such as lowered glycated hemoglobin (A1c) and systolic blood pressure levels. The role extends from medication review to identifying drug–disease interactions, deprescribing, medication simplification, and extended monitoring/follow-up with patients for symptom management. This chapter introduces the definition of a complex patient, outlines the implications of complexity for the patient, and examines the role of the pharmacist in providing care to complex patients. It also addresses current tools used to identify complex patients in practice and presents a guide to complex patient assessment designed for use by pharmacists in various clinical settings.