This dissertation offers a platform to understand the nature of cluster initiatives as a socio-economic phenomenon combining cluster, entrepreneurship and intermediary features. They are particular types of ventures facilitating networks and dialog platforms adjusted to local contexts and offering a way to enhance regional development. The success of clusters and regions is shaped by the degree they are based on and involve entrepreneurial activity, which is viewed here under the prism of cluster initiatives. This dissertation uses both qualitative and quantitative approaches to study various organizational aspects of cluster initiatives and their intermediary role as well as providing recommendations for the management and support of these organizations. It is based on five papers written by the author of the dissertation solely and in collaboration with other scholars where the level of analysis is focused on cluster initiatives. Based on empirical material from the papers this dissertation brings together both the structural and organizational content of cluster initiatives by providing evidence in the areas of actors and relationships, mode of organization and intermediary specific, assessment and management as well as policy. This work has generated the following conclusions: firstly, cluster initiatives represent organizations bringing together a four-faceted constellation of interrelated actors (i.e. the initiative itself, key player, support and target group), through organization of intermediary activities. Secondly, these organizations are organized as temporary projects, but being able to attract many members and to satisfy their needs through diversified and innovative activities can help them to achieve longevity. The longevity of initiatives can also be supported by policy, which in order to become effective, should include a long-term perspective and bottom-up approach. And finally, the study proposes a model of five central qualitative success factors to be used for the assessment and management of the initiatives, which together depict a holistic picture of their functioning. This model contains elements such as idea, driving forces, activities, organization and critical mass. The two models of interrelated actors and of success factors form the main contribution of this work. Extending the stream of studies this dissertation raises awareness and calls for recognition of cluster initiatives as important actors working in-between the boundaries of other organizations and institutions. / PIE/HELIX