Full configuration interaction (FCI) provides the exact solution to the time-independent electronic Schrödinger equation within a finite basis set, by considering the interaction of every possible arrangement of electrons within a molecular orbital space. Unfortunately, FCI scales as O(N !) with respect to molecular and basis set size, making it intractable for molecules larger that a few atoms, even on the most advanced computer hardware. It is possible to reduce the number of configurations considered in CI methods by eliminating all excitations above a given order, though size extensivity issues limit the applicability of truncated CI. In contrast, coupled-cluster theory mitigates this issue by using an exponential ansatz.