The paper reviews the origins and evolution of the Training and Visit (T&V) extension system, which was promoted by the World Bank in 1975-98 in over 50 developing countries. The discussion seeks to clarify the context within which the approach was implemented, and to analyze the causes for its lack of sustainability and its ultimate abandonment. The paper identifies some of the challenges faced by the T&V approach as being typical of a large public extension system, where issues of scale, interaction with the agricultural research systems, inability to attribute benefits, weak accountability, and lack of political support tend to lead to incentive problems among staff and managers of extension, and limited budgetary resources. The different incentives and outlook of domestic stakeholders and external donor agencies are also reviewed. The main cause of the T&V system's disappearance is attributed to the incompatibility of its high recurrent costs with the limited budgets available domestically, leading to fiscal unsustainability. The paper concludes with some lessons that apply to donor-driven public extension initiatives, and more generally to rural development fads. The role of timely, independent, and rigorous evaluative studies is specifically highlighted.