Biosimilars are drugs that are similar, but not identical, to originator biologics. Pre-clinical analytical studies are required to show similarity on a molecular and structural level, but efficacy and safety studies in humans are essential to ultimately determine biosimilarity. In this review written by members of the International Psoriasis Council, we discuss how biosimilars are evaluated in a clinical setting, with emphasis on extrapolation of indication, interchangeability, and optimal clinical trial design. This article is protected by copyright. All rights reserved.