Novel innovation ecosystems and their initiators face the liability of newness, which they need to overcome by creating legitimacy over the new value proposition they are forming. In highly regulated fields, these challenges are highlighted, and gaining legitimacy from both the new entrants and the incumbents requires a balanced approach. This multiple case study investigates the planning processes of four local energy system projects challenging the status-quo. The projects’ internal legitimacy is partly based on advocating loosening up the incumbents’ monopolies. As this outcome requires external legitimacy from the incumbents and other systemic stakeholders, the modes of collaboration with incumbents and new entrants play an essential role. The results of this paper show a revealing interplay between different legitimacy aspects and collaboration modes.