HIV prevention is a global public health priority. Providing efficacious prevention methods that have the greatest likelihood of use will have a profound impact on the public's health. Critical to their use is "acceptability." However, current conceptualizations of adherence and acceptability fail to fully articulate and account for patterns of use and non-use. Formulation properties are critically important to both drug delivery and the user experience. Microbicide developers thus have the opportunity to directly control a formulation's impact on acceptability and adherence to product use, as well as biological product performance. Microbicide products can and should be developed such that they achieve performance standards for both these behavioral (user experience) and biological (efficacy) functions. By incorporating the user experience early on in the product development process, developers will have the greatest chance of providing at-risk individuals with the best prevention methods science can provide. Developing prevention products that can be used in the vagina and/or the rectum and that optimize the user experience in both compartments increases the likelihood that these products will be used consistently and correctly. The impact on global public health has the potential to be far-reaching, decreasing HIV and sexually transmitted infections (STI) incidence and prevalence in both women and men.