Recently, there has been a proliferation of research on the functional independence of two of Skinner's (1957) verbal operants, the mand, and the tact. This research has produced highly variable results. In this article, we provide a critical review of the literature on mand-tact independence, a literature that has implications for both theory and practice. Included in the review are 17 studies with a total of 66 participants who were tested for mand emergence following tact training, tact emergence following mand training, or both, and 11 additional studies that systematically manipulated variables expected to affect the outcomes of such tests. A primary finding is that most studies to date suffer from problems with construct validity. However, it may be justifiable to conclude that the literature provides at least weak support for the functional independence of mands and tacts. Future investigators should avoid the major construct validity pitfalls described in this article, describe participant characteristics more thoroughly, and consider alternative approaches to studying mand-tact independence.