The problem for assessing biosimilarity and drug interchangeability of follow-on biologics (biosimilar products) is studied. Unlike the generic products, the development of biosimilar products is much more complicated because of fundamental differences in functional structures and manufacturing processes. As a result, the criteria and standard methods for the design and analysis of bioequivalence assessment of generic drug products may not be directly applicable to assessing biosimilarity of biosimilar products. In this article, we provide some scientific considerations for criteria, design, and analysis regarding the assessment of biosimilarity and drug interchangeability of biosimilar products. In addition, we discuss scientific and practical issues raised at the 2010 FDA public hearing and the 2011 FDA public meeting on biosimilar products.