Although CASSCF has been used since the 1980s, the prospect of automated active space selection has only received significant attention within the last decade or so. Recently, we published the ranked-orbital approach to select active spaces and the approximate pair coefficient (APC) approximation for low-cost estimates of the orbital entropies used in the ranking. This automated scheme, inspired by the entropy-driven approach of Stein and Reiher, allows for the flexible selection of active space size with a hierarchy of levels (max (8,8), max (10,10), max (12,12)...) reminiscent of the CI level sequence (CISD, CISDT, CISDTQ, ...).