When, if ever, should the executive decline to defend in court a federal law it has concluded to be unconstitutional, and yet still enforce that same statute? The question is presented by the Obama Administration’s decision to enforce, but not defend in court, Section 3 of the Defense of Marriage Act (“DOMA”). But the DOMA § 3 decision is not the first time the executive has bifurcated enforcement of a statute from its defense in court. The practice dates back at least to World War II. Yet the conditions of possibility and the consequences of “enforcement-litigation gaps” have never been specified, investigated, or evaluated. This Article fills that gap. Enforcement-litigation gaps are a form of departmentalism: constitutional practice by a political branch. Reflecting the strong priors many have toward executive branch departmentalism, enforcement-litigation gaps provoke both broad endorsement and strong repudiation. Contrary to conventional wisdom, this Article argues that a categorical response of either kind is unjustified. Enforcement-litigation gaps are neither always justified nor logically inconsistent with larger constitutional values. By clarifying the variables at stake when the executive separates enforcement from litigation, I develop a general framework for distinguishing desirable from undesirable uses of the practice. This framework suggests enforcement-litigation gaps are most justified when the executive defends an Article II value. They rest on weaker footing when the underlying constitutional question relates to the constitutional rights of third parties. The Obama Administration, on this account, acted unwisely in distinguishing the continued enforcement of DOMA § 3 from its defense in federal court—but not for the reasons generally believed.