In this light, selected configuration interaction (sCI) methods have come to the fore, driven by several recent important methodological advances. The goal of selected CI methods is to find sparse approximate solutions to the full configuration interaction (FCI) problem, which is generally done in an iterative manner where the FCI parameter space is efficiently searched, ranked, and top contributors included in the process of obtaining a sparse solution to the CI problem. Most selected CI methods begin by selecting an initial variational space (such as a Hartree-Fock, HF, reference or complete active space self-consistent field, CASSCF, reference) and obtaining the variational ground state wave function within this space. After the initial wave function is obtained, search algorithms explore the space outside the current set of determinants to select important additional determinants to be included in the variational space. The estimated significance of a determinant may be based off perturbative or energetic heuristic considerations. Furthermore, the space may be optionally pruned to eliminate determinants deemed no longer significant. After the searching and pruning, the ground state of the Hamiltonian in this new variational space is obtained. The process is then repeated until some convergence criteria is reached.