Biosimilars are biological drugs that are similar to, and cheaper than other biological drugs (called “reference originator biologics”) that are already in use. They share an identical amino-acid sequence but, given the inherent variability of biological molecules, not full “sameness”. Biosimilar registration follows a strictly regulated pathway based on a totality-of-evidence approach. This article critically discusses the particulars of biosimilar development, including the continuous development of regulatory guidelines, familiarises readers with biosimilar-specific terminology, addresses the typical challenges of writing biosimilar dossiers, and summarises future directions in biosimilar development in the context of a changing competitive landscape. After reading this article, medical writers with different backgrounds, including those previously unfamiliar with key aspects of biosimilar development, should be able to better understand and apply these guidelines in their daily biosimilar work.