This chapter examines the mechanisms and instruments for holding Europol accountable for its activities, in particular as regards its data processing activities. An adequate and effective accountability system is essential to keep Europol in check and ensure that the agency lives up to the requirements and expectations set by its relevant legal-policy framework. The chapter begins with conceptual considerations regarding accountability of EU agencies and of Europol in particular. Next the role of Europol as an expert EU agency is outlined, followed by a general overview of Europol's accountability regime. The chapter then focuses on parliamentary scrutiny (Section 5) as a means of holding Europol politically accountable, followed by the more specialized personal data processing supervision of Europol's activities by expert bodies such as EDPS and national data protection authorities.