This Funding Opportunity Announcement (FOA) invites researchers to submit applications for support of clinical projects that address critical needs for clinical trial readiness in rare diseases. The initiative seeks applications that are intended to facilitate rare diseases research by enabling efficient and effective movement of candidate therapeutics or diagnostics towards clinical trials, and to increase their likelihood of success through development and testing of rigorous biomarkers and clinical outcome assessment measures, or by defining the presentation and course of a rare disease to enable the design of upcoming clinical trials.