The results of recent referendums around the world have concealed an important similarity among many of them: they were not constitutionally required. For example, the UK Constitution does not require a referendum to authorize Brexit nor does the Colombian Constitution require one to ratify the FARC peace pact. Yet in both cases incumbents felt compelled to forego the settled rules of constitutional change in order to bring their reform proposals directly to the people. This is not a rare practice: leaders have often had recourse to referendums by choice rather than obligation as part of a larger strategy to legitimate a major constitutional change. I draw from various non-obligatory referendums to develop a typology of discretionary referendums in constitutional amendment. I examine why constitutional actors use discretionary referendums and situate their use against the backdrop of an increasingly observable phenomenon in democracies: the circumvention of formal amendment rules.