Constitutions obsolesce rapidly, and must be updated over time to reflect changes in the polity's circumstances and citizens' values. What institution or process should be entrusted with the authority to do the updating? If periodic wholesale replacement of the constitution is infeasible, the plausible choices are the constitutional amendment process set out in Article V, flexible interpretation by judges under the banner of constitutional common law, or some mix of the two. Here I explore the question by comparing the relative merits of formal amendments and the constitutional common law as means of constitutional updating. I attempt to dispel some prominent arguments that unjustifiably privilege constitutional common law over the amendment process, and also attempt to sketch the empirical conditions under which either process proves superior to the other. My principal target is a standard academic view that I shall call "the generic case against constitutional amendment." On this view, there are good general reasons to reject, or to indulge a presumption against, any proposed amendment. Among these reasons are the following claims: it is bad to "tamper" with the Constitution; the Constitution should not be "cluttered up" with amendments that will "trivialize" its majesty; constitutional amendments are "divisive" or "polarizing"; constitutional amendments may have bad unanticipated consequences; and constitutional amendments diminish the coherence of the constitutional text or of judicially-developed constitutional doctrine. Something like this view has become the conventional wisdom in the legal academy, following explicit arguments by Kathleen Sullivan and others. I argue that the generic case against constitutional amendment fails. The generic case rests on a nirvana fallacy that implicitly contrasts a jaundiced view of the amendment process with a romanticized view of common law constitutionalism. The real alternative to constitutional amendment is flexible judicial interpretation that updates the Constitution over time - a practice that can also be seen as tampering with or trivializing the Constitution, that is at least as polarizing or divisive as constitutional amendment, that equally risks bad unintended consequences, and so on. Once we have dispelled the nirvana fallacy underlying the generic case against amendment, constitutional updating is seen to pose a comparative institutional question. Constitutional amendment, on the one hand, and constitutional common law, on the other, are alternative institutional processes for managing the inevitable updating of constitutional law over time. Under what circumstances might one process or the other prove superior? What institutional considerations, or variables, determine their relative performance? I consider the strengths and weaknesses of each process: relative to common-law constitutionalism, the amendment process is less focused on the facts of particular cases (both for good and ill); puts less weight on the views of past judges (both for good and ill); allows for the participation of decisionmakers from a broader range of professions and backgrounds (both for good and ill); produces more enduring constitutional settlements, albeit at higher initial cost; and trades the benefits of flexibility for the benefits of rigidity. Amendments show to best advantage, relative to common-law constitutionalism, where the constitutional changes in question involve large value choices as opposed to technical improvements in the law, where constitutional change must be systemic and simultaneous rather than piecemeal, and where irreversible change is more valuable than reversible change.