Haloalkanes and Haloarenes are an important class of organic compounds. These are obtained by replacing a hydrogen atom of an aliphatic or aromatic hydrocarbon by a halogen atom. By replacing a single hydrogen atom, these compounds exhibit vastly different properties and undergo varied reactions as compared to the parent hydrocarbons. These find wide applications in day-to-day life and is used as a starting materials for the synthesis of wide range of organic compounds. In this chapter, we will study about the nature of C-X bond, classification, methods of preparation of haloalkanes and haloarenes, and chemical reactions undergone by them along with their applications.