After initial disclosure of an orbital symmetry explanation for the stereochemistry of electrocyclic reactions in 1965, The Conservation of Orbital Symmetry was published as a review article in Angew. Chem. Internat. Edit. in Engl. in 1969 (ACIEE 1969, 8, 781-853). The publication described the basic features of the theory and all supporting data known at the time, as well as some predictions of the theory that were later verified. Due to its popularity, it was republished in the following year as a booklet by respected academic publishers in the U.S (Academic Press) and West Germany (Verlag Chemie), with a third and final printing in Jan. 1971. Elsevier (of which Academic Press is now an imprint) reissued the booklet in 2014. This is an electronic copy (1200 dpi) with Optical Character Recognition.