In the domain of high-accuracy molecular electronic structure calculations, the move to explicitly correlated methods has sparked a dramatic improvement in the convergence of correlation energy and other properties with respect to basis set size. Previously, methods such as the coupled cluster (CC) approximation were limited by a requirement for large basis sets to reach convergence and simultaneous steep scaling of the necessary computational resources. One solution to this problem has been to use basis sets that systematically approach the complete basis set (CBS) limit, such as the correlation consistent family, 5 and then estimate the CBS limit using extrapolation formulae; with correlation consistent polarized valence n-zeta (cc-pVnZ) basis sets, one can take energies computed with two or more different basis set cardinal numbers, n, and after selecting a suitable extrapolation formula (see, for example, Refs. for more information on such extrapolations) easily produce a CBS estimate. The explicitly correlated (F12) methods offer a different approach, the inclusion of geminal terms that depend on the interelectronic distance greatly accelerate convergence towards the CBS limit.