: Buprenorphine treatment for opioid use disorder is safe and effective, but only a fraction of Americans who need treatment receive it. One reason for this is that many buprenorphine treatment programs have rigid requirements for entry and continuation, limiting the number of people who receive treatment. "Low-threshold treatment" is a term used to describe an alternative approach that attempts to remove as many barriers to treatment as possible. However, few studies have described its essential features. In this article, we define low-threshold treatment and propose the approach be guided by the following principles: same-day treatment entry; harm-reduction approach; flexibility; and wide availability in places where people with opioid use disorder go. We discuss the evidence and rationale for these principles and directions for future research.