Integrating the European electricity markets is among the EU’s most ambitious regulatory endeavours. Important economic and environmental aims depend for their success on continued progress with electricity market integration. In turn, this requires considerable investment in cross-border interconnectors. Nevertheless, numerous European countries have established statutory monopolies that restrict interconnector investment to a monopolist. The resulting restrictions on third-party investment were a core issue underlying the recent Aquind case. Against this backdrop, it is surprising that these statutory transmission monopolies have so far passed largely under the radar, in terms of both adjudication by the European courts and also discussion in the literature. This article argues that statutory transmission monopolies are overlooked, illegal relics from a pre-liberalised past. Regulators, such as the Commission, as well as affected stakeholders, should challenge statutory transmission monopolies where they impede interconnector investment. Based on the existing case law, free movement law appears as the tool of choice in this context.