Promoting Readiness of Minors in SSI (PROMISE) was a federal initiative to support youth receiving Supplemental Security Income (SSI) during the transition to adulthood. This article discusses insights gained from the national PROMISE evaluation about the current transition system. The national evaluation relied on a randomized controlled trial design and information obtained from staff interviews, surveys of parents and youth, and program administrative data. The authors found that: (1) many SSI youth received transition services without PROMISE, but that there was substantial room for PROMISE to improve service use; (2) intensive case management, facilitating early work experiences, and a family focus were the primary PROMISE innovations to usual services; (3) formal partnerships enhanced interagency collaboration but required time to form, service benchmarks, and regular communication; (4) identifying SSI youth for outreach is challenging under the current system; (5) PROMISE service costs represented relatively large investments; and (6) the intensive case management offered by PROMISE might be difficult to sustain in the current system. Lessons from PROMISE are relevant to current initiatives supporting youth with disabilities during the transition to adulthood. The evaluation will assess the longer-term impacts of PROMISE and provide information about its potential for generating long-term benefits.