Abstract: This paper was prepared for a conference about constraints on executive discretion. In addition to law and politics (to whatever extent they do or do not constrain the executive), there is also a distinct third bound on executive discretion: conventions, roughly understood as unwritten but obligatory rules of the political game. Debates over executive discretion should take account of distinctions between contingent politics and conventions; between intragovernmental conventions and extragovernmental conventions; and between conventions against doing things and conventions against saying things. The last distinction, in particular, illuminates the strong resistance, in contexts such as immigration, to executive policy statements that make explicit a pattern of enforcement discretion, one that would otherwise remain only implicit. Even holding legal authority constant, making that authority explicit through general policy statements may trigger the normatively-inflected political sanctions that are characteristic of conventions.