Since the approval of the first biosimilar, Omnitrope, biosimilars have been authorized in many jurisdictions, including Australia, Canada, Japan, Korea, the US, and many other countries. Subsequent-entry biologic (SEB) is the Canadian term used for a biosimilar that enters the market subsequent to a Canadian biological drug previously authorized in Canada. This chapter deals extensively with the underlying science that was the basis of the Canadian approach to regulating biosimilars. In particular, it discusses quality, clinical and statistical aspects of biosimilar development, and their importance for the consideration of extrapolation of indications. Extrapolation of indications is possible when the appropriate data and rationales are provided. Recently, a new amendment to the Food and Drugs Act, Bill C-17, also called Vanessa's law, has provided the regulator with added authorities such that it is now possible to take a lifecycle approach to the regulation of any drug product in Canada, including biosimilars.