Abuse-deterrent opioid formulations are receiving renewed interest in light of the increasing legitimate medical use of prescription opioids for the adequate treatment of pain. Unfortunately, there is an inevitable associated potential for misuse, diversion, and abuse. The challenges of deterrence are significant: opioid abusers are a heterogeneous population; studies on drug "liking" and opioid "attractiveness" are informative, but mainly rely on reports from users who are not reliable respondents; drug "liking" scores are useful, but it is unclear how much drug "liking" must be reduced in order to achieve an actual reduction in abuse levels; and the most popular drugs among opioid abusers appear to be those that meet a complex combination of both positive and negative criteria including things like availability, pricing, and how easily the drug's illicit use can be concealed. Several abuse-deterrent formulations have been introduced or are in development. Epidemiological studies will have to be conducted to evaluate their effectiveness. Although there are currently more questions than answers, such products are clearly of medical and societal importance.