Many people hope that evidence — be it lived experience, clinical know how, or scientific research findings – can be used to improve policies towards addictive drugs, addiction, treatment, and recovery. But public policymaking can seem mysterious and irrational, such that many are cynical that evidence can matter. This presentation describes how even though many factors other than evidence shape public policy, evidence can exert some influence and sometimes a great deal of influence. After detailing what counts as evidence and how evidence is different than opinions and values, this presentation walks through actually policy changes in which they author was involved, including the 2008 campaign for mental health and addiction parity in health insurance and the 2010 passage of the Affordable Care Act. Each case study illuminates when evidence mattered and in what way, emphasizing that while evidence can’t and shouldn’t carry the day in a democracy, it has unique value both for the design and passage of policy as well as its implementation.