Classification of agroforestry (AF) systems is necessary in order to provide a framework for evaluating systems and developing action plans for their improvement. The AF Systems Inventory (AFSI) being undertaken by International Centre for Research in Agroforestry (ICRAF) provides the background information for an approach to classification. The words 'system,' 'sub-system' and 'practice' are commonly used in AF literature. An AF system refers to a type of AF land-use that extends over a locality to the extent of forming a land utilization type of the locality. Sub-system and practice are lower-order terms in the hierarchy with lesser magnitudes of role, content and complexity. In common parlance, however, these terms are used loosely, and almost synonymously. Several criteria can be used to classify and group AF systems (and practices). The most commonly used ones are the system's structure (composition and arrangement of components), its function, its socio-economic scale and level of management, and its ecological spread. Structurally, the system can be grouped as agrisilviculture (crops - including tree/shrub crops - and trees), silvopastoral (pasture/animals + trees), and agrosilvopastoral (crops + pasture/animals + trees). Other specialized AF systems such as apiculture with trees, aquaculture in mangrove areas, multipurpose tree lots, and so on, can also be specified. Arrangement of components can be in time (temporal) or space (spatial) and several terms are used to denote the various arrangements. Functional basis refers to the main output and role of components, especially the woody ones. These can be productive functions (production of 'basic needs' such as food, fodder, fuelwood, other products, etc.) and protective roles (soil conservation, soil fertility improvement, protection offered by windbreaks and shelterbelts, and so on). On an ecological basis, systems can be grouped for any defined agro-ecological zone such as lowland humid tropics, arid and semiarid tropics, tropical highlands, and so on. The socio-economic scale of production and level of management of the system can be used as the criteria to designate systems as commercial, 'intermediate,' or subsistence. Each of these criteria has merits and applicability in specific situations, but they have limitations too so that no single classification scheme can be accepted as universally applicable. Classification will depend upon the purpose for which it is intended. Nevertheless, since there are only three basic sets of components that are managed by man in all AF Systems, viz. woody perennials, herbaceous plants and animals, a logical first step is to classify AF systems based on their component composition, into agrisilivcultural, silvopastoral and agrosilvopastoral (or any other specialized) systems. Subsequently the systems can be grouped according to any of the purpose-oriented criteria. The resulting system name can thus have any one of the three basic categories as a prefix; for example agrisilvicultural system for soil conservation. Some of the major AF systems and practices of the tropics are grouped according to such a framework. The scheme appears a logical, simple, pragmatic and purpose-oriented approach to classification of AF systems.