In an age of expertise, where knowledge ostensibly reigns, global governance not infrequently settles for ignorance. To understand this puzzle, this article draws upon extensive empirical research on two sites within the global governance of finance. One is directed to the suppression of money laundering and combating the financing of terrorism by the Financial Action Task Force and International Monetary Fund. Another intends to stimulate the supply of otherwise scarce money to financial markets through global lawmaking by the UN Commission on International Trade Law. In both cases vast enterprises of global regulation and lawmaking proceed on weakly founded justificatory rhetorics designated here as 'plausible folk theories.' Six properties make a folk theory plausible: parsimony, face validity, rhetorical compactness, ambiguity, affinity with extant beliefs, and unexamined premises and logics. Plausible folk theories offer organizational benefits to IOs. They also allow a politics of temporality that may shorten temporal horizons, or weaken and eliminate IO accountability. Finally, three variants of ignorance contribute to choices by international organizations not to get beyond plausible folk theories to justify their regulatory and lawmaking initiatives: inadvertent ignorance, willful ignorance, and strategic or rational ignorance.