First deployed in 2005, the competitiveness cluster policy sought to develop local innovation ecosystems and more extensive networks by selecting clearly defined themes and regions. These clusters used a variety of tools, particularly subsidies awarded to finance collaborative R&D projects involving enterprises and research and training bodies. This article assesses the effects of participation in clusters on Small and Medium Enterprises (SMEs) and Intermediate Enterprises. Not all these enterprises participated in a subsidised project, so this assessment measures a mixture of the effect of participation in a collaborative project and the effect of participation in a competitiveness cluster without a project. Competitiveness clusters were set up against a backdrop of strong state support for R&D: the increase in the total amount of Research Tax Credits (Crédit d'impôt recherche - CIR) from €1 billion to €5 billion between 2005 and 2009 played a decisive role. Participation in the clusters cannot be dissociated from growth in the CIR, because companies were able to combine subsidies with the CIR to finance their R&D projects. The effects measured in this study correspond to those of participation in clusters and their possible amplification thanks to the sharp rise in the CIR. In 2009 the SMEs and intermediate enterprises belonging to clusters spent an average of €116,000 more on R&D than similar companies not belonging to the scheme. This amount is roughly equivalent to the extra government aid they received in the form of subsidies and CIR: there does not appear to have been either a windfall effect or a knock-on effect on private-sector R&D expenditure. This rise in R&D expenditure led to an increase in R&D jobs. However, as things stand, there does not appear to have been an increase in revenues or in the number of patents registered.