Cost-benefit analysis (CBA) is usually treated as a monolith. In fact, the term can refer to a broad variety of decision making practices, ranging from a qualitative comparison of pros and cons to a highly formalized and technical method grounded in economic theory that monetizes both costs and benefits, discounts to present net value, and locates the point at which the marginal benefits curve crosses the marginal costs curve. This article develops a typology that helps to conceptualize the multiple varieties of CBA along a formality-informality spectrum. It then uses this typology to analyze the treatment of CBA by the academic community and the three branches of the federal government. In academic and policy circles, the formal end of this spectrum generates far more controversy than the informal end. Additionally, the law (federal environmental statutes and case law) seems to favor informal over formal varieties of CBA. Nonetheless, the executive branch appears to be moving toward the formal end of the spectrum. Executive Orders and guidance documents direct agencies to conduct a highly formal mode …