In the battle for control of COVID-19, we have few weapons. Yet contact tracing is among the most powerful. Contact tracing is the process by which public health officials identify people, or contacts, who have been exposed to a person infected with a pathogen or another hazard. For all its power, though, contact tracing yields a variable level of success. One reason is that contact tracing’s ability to break the chain of transmission is only as effective as the proportion of contacts who are actually traced. In part, this proportion turns on the quality of the information that infected people provide, which makes human memory a crucial part of the efficacy of contact tracing. Yet the fallibilities of memory, and the challenges associated with gathering reliable information from memory, have been grossly underestimated by those charged with gathering it. We review the witness and investigative interviewing literatures, identifying interrelated challenges that parallel those in contact tracing, as well as approaches for addressing those challenges.