Sociological studies of organizational fashions tend to focus on commercial firms. This article looks at the Capacity Development concept that is globally applied as a model in governmentally supported development assistance organizations. The organizations themselves adopt the concept, asserting that an increase in ‘capacities’ in developing countries will contribute to a higher success rate for projects. This article argues that a primary function of concepts such as Capacity Development is to meet the legitimacy requirements of development assistance organizations. The more the effectiveness of these organizations is criticized or challenged, the more they feel the need to defend themselves by developing new — and hopefully more effective — concepts.