The US Food and Drug Administration (FDA) was authorized in 1984 to approve generic drug products under the Drug Price Competition and Patent Term Restoration Act, which is known as the Hatch–Waxman Act. In Canada, the term substitutability is applied to two products that can be used in lieu of the other during and within the same treatment period, that is, for interchangeability as discussed in this chapter. The general guidance of Health Canada on biosimilars does not consider explicitly interchangeability. The situation is entirely different in considerations of interchangeability of biological products. First, the terminology has become regrettably confusing. In the United States, the BPCI Act introduced the terms of switching and alternating without providing clear interpretation. The EMA has issued product-related guidelines for biosimilars, as well as a general guideline in 2014, and has approved a large number of biosimilars. The consideration of interchangeability requires additional demonstration; the conditions for these have not yet been clarified.