The aim of the present review article is to introduce some of the methods used in theoretical studies of molecular potential surfaces for chemical reactions. Some of the basic equations relevant to studies of this kind are presented, and applications to some thermal unimolecular reactions are discussed. Three degenerate rearrangements are included: the conversion of methylenecyclobutane into itself, the analogous rearrangement of methylenecyclopropane, and the Cope rearrangement of 1,5-hexadiene. Results are also presented from studies of dimerization and insertion reactions of silylenes. Furthermore, possible species resulting from the reaction between F- and acylsilanes are presented. Finally, some of the computational and methodical problems met in studies of chemical reactions are discussed.