This overview is composed of four major sections. Part I is a map of agricultural extension's "territory," that is, the definitions and systems. It discusses extension functions in agricultural production institutions and varying institutional settings, describes types of extension systems, and considers farmers' degree of influence on extension systems and multiple extension systems. Part II analyzes national arrangements for extension. A chart presents an overview of national arrangements and compares these with extension system approaches and their relationship to farmers. Public sector and private sector extension are then discussed separately. Part III is a critical review of recent developments relating to extension, including focus on private sector provision, privatization of public extension systems, trend among large farmers to bypass public extension services, research institutions' efforts to provide "frontline extension," development of new designs and mechanisms for linking research and extension, search for participatory methods, and experimentation with hybrid research-extension systems. Part IV recommends four directions or priorities for the future: development policy goals, national arrangements for institutional change, extension agency development, and social science research requirements. (YLB)