The recent announcements of the Ontario Basic Income Pilot and Finland's cash grants to jobless persons reflect the growing interest in some form of guaranteed annual income (GAI). This idea has circulated for decades and has now been revived, no doubt prompted by concerns of increased inequality and employment disruptions. The Manitoba Basic Annual Income Experiment (Mincome), conducted some 40 years ago, was an ambitious social experiment designed to assess a range of behavioural responses to a negative income tax, a specific form of GAI. This article reviews that experiment, clarifying what exactly Mincome did and did not learn about how individuals and households reacted to the income guarantees. This article reviews the potential for Mincome to answer questions about modern-day income experiments and describes how researchers may access these valuable data.