This chapter outlines several issues of carbon science and technology that are essential to understand the origins, preparation, characterization and applications of activated carbon. Activated carbon is a unique material; it is a member of a family of carbons ranging from carbon blacks to nuclear graphites, from carbon fibres and composites to electrode graphites, and many more. All come from organic parent sources but with different carbonization and manufacturing processes. The availability of activated carbon for industrial use has much to do with accessing resources, renewing resources and processing to rigid specifications to control specific industrial applications. Activated carbon does not just happen; it has to be synthesized. The porosities of a carbon, as initially prepared by carbonization, are not sufficiently developed for most applications and some amelioration is a prerequisite step. This is done in several ways involving creation of further porosity, widening of existing porosity, modifications to the surfaces of porosities and also modifying the carbonization process itself. Additionally, to the main processes of activation by carbon dioxide or steam, three other techniques of chemical activation are used, involving co-carbonization with (a) zinc chloride, (b) phosphoric acid and (c) with potassium hydroxide.