Addiction has been scientifically established as a disease, not an absence of willpower. Neuroscientists are studying how drugs of abuse alter the brain, animal models are guiding us to new knowledge at the molecular level, and genetic tests are helping to distinguish many forms of addiction. With such research comes hope for better prevention strategies, more effective pharmaceutical regimens, reduced stigma, and new guidelines for achieving lasting recovery. Ironically, some of the future drugs to treat addiction may come from the very companies that also sell drugs that addict, such as painkillers. Is that an ethical problem? Where is the latest science taking us, and what does it mean for treatment? How do we measure success?