With growing recognition of the potential value of microbicides for HIV/STI prevention, the importance of the acceptability of this brand-new technology has been widely acknowledged. We review the current body of microbicide acceptability research, characterize the limitations in assessment approaches, and suggest strategies for improvement. Electronic databases and abstracts of recent meetings were searched for acceptability data regarding vaginal and rectal products that may be used for HIV prevention. Of the 61 studies reviewed, more than half assessed acceptability based primarily on the description of a hypothetical microbicide, or with the demonstration of a spermicide or lubricant. Physical characteristics of microbicidal products, their effects after insertion, and their effects on sensation during intercourse (for both partners) were the dimensions most frequently assessed (measured in 77%, 49% and 49% of studies, respectively). Attention to the social context of use was inadequate. As acceptability is likely to be a key determinant in the use-effectiveness of microbicides, in-depth understanding of the social processes that shape microbicide acceptability across diverse populations will become increasingly valuable. This includes exploring the effects that sexual partners, health care providers, and key opinion leaders have on the acceptability of microbicides among women and men, including youth and people living with HIV. Future research will benefit from studies of the acceptability of other contraceptive-barrier methods (especially the female condom), use of an agreed-upon operationalization of acceptability, use of acceptability assessments within clinical trials, expansion of measurement domains, and assessment of changes in perceptions of acceptability and use over time. Failure to understand the key factors associated with microbicide acceptability is likely to hinder the adoption and continued use of products that are effective in preventing HIV infection.