The new National Institutes of Health (NIH) Policy on the Use of a Single Institutional Review Board (sIRB) for Multi-Site Research was adopted primarily to simplify and speed the review of complex multisite clinical trials. However, speeding review requires overcoming a number of obstacles. Perhaps the most substantial obstacle is the time and effort needed to develop reliance agreements among the participating sites. We conducted 102 semistructured interviews with sIRB personnel, including directors, chairs, reviewers, and staff, from 20 IRBs that acted as sIRBs for multisite research, including 6 commercial/independent sIRBs, and 10 university-based academic and 4 federal sIRBs. Almost without exception, the interviewees agreed that reliance agreements were complex, difficult to develop, and time-consuming. A major problem for relying sites was that different agreements specified different responsibilities for the relying sites. Attitudes differed about whether these problems will be resolved as IRB staff and managers become more experienced with sIRBs. However it is clear that the process of developing reliance agreements must be simplified. Federal assistance in standardizing at least some sections of reliance agreements might reduce the difficulties involved.