This chapter outlines the developments in the chemistry of acyclic and monocyclic monoterpenoids that have taken place between 1973 and 1992. A representative overview is provided and reactions related to general applications are discussed. The chapter also explores biotransformation reactions, the conversion of acyclic monoterpenoids into cyclic systems, and applications of monoterpenoids as chiral reagents and auxiliaries for asymmetric synthesis. A brief discussion of the novel polyhalogenated monoterpenoids, which have been isolated from marine sources, is presented. In addition, the chapter provides an overview of the developments in the field of study of the conversion of acyclic monoterpenoids into cyclic. Illustrations are also provided for the biotransformation of monoterpenoids, which can be affected by bacteria or by fungi.