The Biologics Price Competition and Innovation Act of 2009 (BPCI Act) created an abbreviated licensure pathway in the United States that allows for the development and approval of biologic products shown to be biosimilar to or interchangeable with a US Food and Drug Administration (FDA)-licensed reference product. FDA released the draft guidance for industry on Demonstrating Interchangeability with a Reference Product (hereafter referred to as the Draft Interchangeability Guidance) in January 2017. Despite FDA's efforts, there continues to be a great deal of confusion and misinformation surrounding the topic of interchangeability. Here we discuss interchangeability, as well as substitution of biological products, with a focus on the US. Additionally, the separate topic of physician-mediated switching is covered and distinguished from interchangeability and substitution.