The opioid epidemic is the greatest public health crisis of our time. It is estimated that about 64,000 people died of opioid overdoses in 2016 – more than died in the Vietnam war or in 1 year at the height of the AIDs epidemic. Dan Ciccarone, our guest this week, and a Professor at UCSF School of Medicine, has spent his career trying to improve our understanding of substance use disorders and their health consequences. He and his collaborators look at this question both up-close, through ethnographic research in the community, and hours and hours of interviews with people who use injection drugs, and also by stepping back and sifting through huge datasets, looking at the larger epidemiologic and economic forces shaping the epidemic. He has spent years studying heroin specifically, and is currently the PI of the Heroin in Transitions study, which continues this vital work.