Chemical building blocks in quantum chemical calculations.: Perspective on "The density matrix in many-electron quantum mechanics I.: Generalized product functions.: Factorization and physical interpretation of the density matrices" -: !McWeeny R (1959) Proc R Soc Lond Ser A 253:242-259

The group function theory described in the title paper of McWeeny is overviewed by pointing out its influence on different fields of theoretical chemistry, in particular its serving as a general framework for various forms of building blocks and local treatments of extended systems.