In the realm of GTOs, the cc-pVXZ and aug-cc-pVXZ basis families of Dunning, Peterson and coworkers have been designed to recover most of the correlation energy due to the valence electrons. More precisely, these are called correlation-consistent since the basis functions that are added at each level of cardinality X=D,T,Q,... contribute with similar amounts of energy, independently of their type (s,p,d,...) and in a consistent manner even in the presence of polarization or diffuse functions. All these are optimized so as to maximize their contributions to the atomic correlation energy. For example, to balance the set, s and p functions are added when the polarization space is extended, so that the correlation energy error due to the s and p functions does not exceed the error from the polarization space. The exponents of such s and p functions are optimized with respect to atomic HF energies, while the correlating polarization functions come from valence energy minimization at the atomic CISD level of theory. The aug-cc-pVXZ bases are derived from the original cc-pVXZ, with the addition of one diffuse function per angular momentum present in the set, and whose (smaller) exponents are determined by minimizing the atomic CISD energy of anions. Although first intended for a better description of electron affinities, the aug-cc-pVXZ basis family has been shown to progressively enhance the convergence of other molecular properties such as proton affinities , dipoles and polarizabilities , or energies of weakly bound systems .