In spite of the growing interest in cluster initiatives (CIs) as a means of regional development, there are still few studies of CIs that offer an inside perspective. This article takes such an inside perspective, focusing on the internal legitimacy aspects of the formation and evolving processes of CIs. We propose the inclusion of interpartner legitimacy effects in order to better understand the formation and development of CIs. A case study method is applied on a Swedish CI in the tourism industry. Faced with the situation that their region was lagging behind other Swedish regions in the development of tourism, the actors were spurred to promote a CI. Its central purposes were to consolidate the regional tourism industry, strengthen the regional brand and to establish the entire region as a single coherent destination. This paper contributes to the research body of regional development and CIs by showing how different types of interpartner legitimacies hinder and facilitate the CI process.