In this paper we portray a specific type of knowledge which we term ‘nomadic knowledge’. It is required periodically by different actors and travels along foreseeable paths between groups or communities of actors. This type of knowledge lets us question generally held assumptions about the way knowledge is enacted. We illustrate our point with an ethnographical field study analyzing the European Social Forum (ESF), a network of political activist organizations. In this network different actors organize a periodic (biannual) event in which some 13,000 activists participated in 2008. We investigate how knowledge about organizing and managing the ESF is transferred between two events respectively, the actors and communities involved. Our study highlights the specific challenges in sharing nomadic knowledge and the consequences of deficiencies on the organizing process. The paper contributes to a better understanding of knowledge sharing practices and opens new directions for technica...