Heterocyclic chemistry is of the utmost practical and theoretical importance. Heterocyclic compounds are in use as pharmaceuticals, dyes, pesticides, herbicides, plastics, and for many other purposes; the industries producing and researching into these products provide employment for a large fraction of all chemists. On the theoretical side, heterocyclic chemistry has provided a host of interesting con- cepts and structures. Yet, the subject is often deprived of the im- portance it deserves; it is said that it is possible to complete work at graduate schools of some universities without having attended a lec- ture course dealing specifically with heterocyclic chemistry