Background:Federal Law requires approval from an Institutional Review Board prior to conducting human subjects research to ensure ethical distribution of benefits and harms. Notwithstanding this role and almost no prescriptive requirements about design or operation, there is little systematic research describing the key attributes of IRBs, as reported by IRB personnel themselves. Methods: Here, 55 IRB directors completed a survey of 77 questions. The goals of the study were to establish what a typical US IRB “looks like,” determine whether IRB characteristics can be summarized by a smaller number of overarching components, determine the best predictors of IRB speed and efficiency, and determine whether IRBs differ by high-level qualitative characteristics such as institution type. The above was explored and tested using the general linear model and principal components analysis, and for the former, dependent variables of interest were, a) the time necessary for an IRB to approve a study, and b) efficiency of the review process for full board and expedited reviews. IVs of interest included multiple IRB characteristics. Results: 1) IRB characteristics can be summarized by four key components; 2) IRB speed and efficiency are most strongly determined by tendency to receive biomedical submissions, especially drug-related; and 3) IRBs do vary by institution type on some key variables. Conclusion: These results are the first step toward establishing national norms and building a working model of US IRBs to which other IRBs can compare themselves.