The National Research Council was tasked with investigating the problem and recommending a set of best practices for measuring these crimes in BJS's household surveys. The first part of the report presents information on the methodology and vehicles currently used to measure rape and sexual assault. The report also examined the NCVS to determine if its structure contributes to the problem of underreporting of rape and sexual assault. The examination found that the structure of the survey does not lend itself to measuring the low incidence events of rape and sexual assault with the precision needed for policy and research purposes. The survey also has problems with retention of participants over the long-term, leading to inaccurate estimate of these crimes. The wording and place of questions about rape and sexual assault were also found to be problematic, preventing them from being answered correctly, if at all. Based on these and other findings, the report presents a set of 10 recommendations for improving reporting of these crimes on national surveys. These include developing an independent survey just for measuring rape and sexual assault, BJS should continue to publish annual estimates of rape and sexual assault criminal victimizations using the recommended new survey to do so; the new survey should have a longitudinal structure; the new survey should be conducted in a self-administered mode; and BJS's definition of rape and sexual assault should be expanded to include incidences when the victim does not have the capacity to consent to the sexual actions of the offender. Continued research on this topic is recommended. Tables, figures, and appendixes