This paper studies the role played by the features of the local knowledge base and the regional environmental support in the entry of new green tech-based firms. We compute a set of specific knowledge indicators which capture the recombination of technologies that make up green technologies in French départements (NUTS3 regions) for the period 2003–2013. By using a rich and unique dataset based on firm-level microdata and patents information, we find that the main determinants of the entry of new green tech-based firms are: (i) the combination of high levels of internal coherence with sufficient diversification into unrelated technological categories other than green and (ii) the regional efforts to reduce the environmental impact of economic activities. Indeed, by applying spatial econometrics we found that the impact of knowledge spillovers mainly accrues within the département of entry. These results suggest that more attention should be paid to the context-specific recombination of technologies constituting green technologies and that environmental regulations may have, an indirect, but important impact when it comes to promote green technological entry in regions.