Inclusion Criteria: Prospective cohort patients: - Diagnosis date must occur on or after March 24, 2011 (date of ipilimumab approval in US) - Diagnosis of stage III (unresectable) or stage IV melanoma (includes mucosal, uveal acral-lentiginous, leptomeningeal disease) - Age ≥ 18 years at time of entry into study - Patients must be actively receiving or scheduled to receive systemic treatment (any line, eg, first, second, third line [including investigational drugs]). - For patients initiating new treatment, treatment must be started within 28 days after signing informed consent. - For patients currently receiving treatment, patients must enroll within the first 21 days of starting new treatment Retrospective cohort patients: - Patients with diagnosis of confirmed unresectable stage III or stage IV melanoma (including mucosal, uveal, acral-lentiginous, leptomeningeal disease) - Age ≥ 18 years at time of unresectable or metastatic melanoma diagnosis - Initiated therapy for unresectable or metastatic melanoma within 4 years prior to approval of ipilimumab (first immune checkpoint inhibitor therapy approved in US) - March 25, 2007 - March 24, 2011 - One year of follow-up data is required from date of therapy initiation, if a patient passed away within the one year of follow-up; such patients are still eligible and the date of death will be collected. 1. If retrospective patients have at least one year of follow-up data and are then treated with immuno-oncology, immune checkpoint inhibitor therapy, or targeted therapy, these patients will be analyzed separately. Exclusion Criteria: Prospective patients: - Patients participating in a clinical study that does not allow enrollment into a non interventional study or clinical studies in which the investigational treatment is blinded - Patients who started new treatment > 21 days - Patients who enrolled in study but did not initiate treatment before 28 days - Patients with current malignancies (except non-melanoma skin cancer and the following in situ cancers: bladder, gastric, colon, endometrial, cervical/dysplasia, melanoma, or breast) that requires additional systemic therapy