This paper is based on the author’s experiences gained during 39 years involvement in technology transfer, focussing on his work as an agricultural consultant in some 30 developing countries. It outlines the main agencies participating in this task and discusses the challenges and constraints, and finally makes some observations about ways to improve the effectiveness of aid programmes. The principal conclusions drawn are that, in general, technology cannot be effectively transferred without adaptation to local conditions, and this process must be guided by an understanding of the whole farming system environment of the target area. This includes the obvious technical, economic and financial constraints and attributes, its infrastructure and institutional capability, as well as the underlying root causes hindering uptake by producers, that are often deeply embedded in the cultural and political characteristics of the country or region.