Biologics have made groundbreaking treatments possible, for several difficult to treat conditions. However, they are very expensive, and biosimilars are expected to push prices down like the generics of small molecule drugs did in the past, replacing more costly brandname drugs. Biosimilars are not just generic replacement for brand name biologics, and their effect on cost reduction will be much more modest. Biologics, made from living organisms, are much larger in size and complex molecules than small molecule drugs which are easily synthesized, characterized and copied. Biosimilars may be highly similar to the original licensed biologic product but not a fingerprint copy; therefore, some differences are expected. This article describes the criteria for establishing similarity and interchangeability, current regulations and the clinical and pharmacoeconomic aspects of the four FDA approved biosimilars in 2015 and 2016.