Plaque psoriasis is a chronic skin disease affecting 1-3% of US and European populations and severely impairs quality of life. Four biologics are authorized in Europe and the US for treatment of patients with moderate to severe psoriasis. Because complete skin clearance is rare with these agents, the treatment goal adopted by regulatory and reimbursement agencies is the proportion of patients achieving at least a 75% reduction from the subject's baseline PASI (Psoriasis Area and Severity Index) score or similarly, a sPGA [static Physician's Global Assessment) score of 0 or 1. Specifically, this study will provide information on the effectiveness of approved biologics as they are used in clinical practice. This information is currently not consistently available from other sources, including existing psoriasis patient registries.