We use the techniques of perturbation theory and the electronic polaron to classify and obtain explicit formulas for electronic correlation in nonmetals. We consider explicitly the case in which the highest valence band is $p$ type and the lowest conduction band is $s$ type or vice versa, a situation which holds for all rare-gas solids, alkali halides, and most semiconductors of the types II-VI and III-V. We consider the case of an electron in a filled band as well as that of an electron in an otherwise empty band. In the case of the electron in an otherwise empty band our formulas are the expression found previously by Inoue, Mahutte, and Wang. Numerical results are presented for electrons both in occupied and otherwise empty bands for a number of crystals.