The EU’s development of advanced instruments and processes of police cooperation on both policy and operational fronts presents new challenges and opportunities for conventional approaches to police accountability and transparency. Although no substantive mention is made of police accountability under Title V of the Lisbon Treaty 2009, it can be expected that the EU’s common transnational measures draw upon, reconcile and enhance Member State approaches to police accountability which are rooted in long-standing constitutional, legal and administrative traditions and values. This chapter will consider whether and to what extent various Member State norms on police accountability and transparency are informing the concept, design and operation of the EU policing regime and vice versa. More particularly, it will recommend the development of a new ethos of ‘transnational police accountability’ which should guide and shape EU policymaking in this area.