1988: Extension is a professional communication intervention deployed by an institution to induce change in voluntary behaviours with a presumed public or collective utility.[7]
1999: The essence of agricultural extension is to facilitate interplay and nurture synergies within a total information system involving agricultural research, agricultural education and a vast complex of information-providing businesses.[9]
2004: Extension [is] a series of embedded communicative interventions that are meant, among others, to develop and/or induce innovations which supposedly help to resolve (usually multi-actor) problematic situations.[10]
van den Ban, A. (1974) Inleiding tot de Voorlichtingskunde, (Dutch edition first published by Boom, later quoted in English editions: 1988, van den Ban and Hawkins, and 2004, Leeuwis and van den Ban)
Nagel, U. J. (1997) Alternative Approaches to Organizing Extension, in Swanson, B. 「Improving Agricultural Extension: A Reference Manual" (3rd Edition)」 FAO
Jones, G.E. and Garforth, C. (1997) The history, development, and future of agricultural extension in Swanson, B. 「Improving Agricultural Extension: A Reference Manual (3rd Edition)」 FAO