The EU’s internal electricity market is founded upon the assumption that a competitive EUwide market is the most efficient means of ensuring the availability of sustainable electricity to all Europeans. This approach requires willingness on the part of Member States to surrender the traditional pursuit of energy autarky in exchange for efficiency and competitive prices. This shift from national independence to greater interdependence requires mutual trust between EU Member States. The article analyses the role of the principle of mutual trust in ensuring the security of electricity supply in the internal electricity market. This legal analysis is conducted using capacity mechanisms as a topical example of how the principle of mutual trust is integrated in the structures of EU energy law and how ensuring the uninterrupted availability of affordable electricity can be used to justify limitations on mutual trust.