The present research aimed at understanding the process by which firms in a cluster start to export based on systemic interactions, and the process of diffusion of exporting as a business strategy within the cluster. Diffusion was defined, following Rogers’ (1995: 5) seminal work, as ‘the process by which an innovation is communicated through certain channels over time among the members of a social system’. The research method used was industry case studies and the unit of analysis selected was the cluster. Two manufacturing industries were chosen to be investigated, and within each geographic area clusters were identified as the origin of dynamic export growth in the industry. Players in each industrial cluster, as well as other significant actors, were interviewed. Extensive secondary data research was done to study clusters’ historical development. Detailed analysis and a comparison of the experiences permitted the extraction of some general conclusions concerning the similarities and differences between the clusters in terms of the adoption and diffusion of exporting. Results showed that the diffusion of exporting in an industrial cluster is quite similar to the dissemination of technical innovation. Social ties were important to facilitate the diffusion of exporting in one of the clusters studied. Also, the role of domestically-owned flagship firms in leading the internationalization process proved to be important in only one of the clusters, while the role of external actors was fully supported in the two industries studied. Finally, a number of support institutions, private and public, interfered in different stages of the internationalization process. In both industries, the federal government had only a late and limited impact on export initiation and development.