The discovery of effective interventions to prevent or delay disability in older persons is a public health priority. Most likely to benefit from such interventions are frail individuals who are not yet disabled and those with early disability who are at high risk of progression. In spite of this frail older persons have often been excluded from research on the assumption that they would not tolerate testing or benefit from treatment. The Interventions on Frailty Working Group developed recommendations to screen, recruit, evaluate, and retain frail older persons in clinical trials. Specific recommendations are: Eligibility screening should include a multistage process, to quickly exclude those who are too well and those who are too sick. Inclusion criteria should target those most likely to benefit, be meaningful to clinicians, and reflect advancements in the frailty research area. Disability outcome measures should include self-reported, objective, and proxy measures. Strategies to improve retention and compliance and to monitor their effectiveness should be an integral part of the study design. Estimation of cost and sample size should contemplate high dropout rates and interference by competing outcomes. Additional research is needed to refine criteria for screening frail older persons, identify objective measures of disability that are reliable and valid in frail older persons, and improve the informed consent process for high-risk participants, recognizing that research in this subgroup is essential to improving their health outcomes.