This chapter explores the accountability of the Banking Union in light of fundamental principles of European Union law. The allocation of supervisory powers to the SSM gives the ECB unprecedented discretionary powers. For instance, the ECB might have to balance the potentially conflicting policy objectives of financial stability and monetary policy or to apply broadly phrased criteria when deciding whether an institution needs to be resolved. On the basis of a fresh look at the democratic legitimacy of independent institutions, the chapter argues that these powers call for a high level of ECB accountability. The question is whether the current structure of the SSM meets this standard. While SSM decisions are subject to legal review, the courts need to respect the discretionary powers of the SSM. Parliamentary accountability via the Banking Dialogue, the focus of much recent research, does not fully make up for this shortcoming. Instead, intra-executive accountability, an underrated dimension of checks and balances, has considerable potential. This concerns in particular the relationship between the SSM and the Commission, and the SSM and the European Court of Auditors. The chapter suggests how one might further strengthen intra-executive accountability in the Banking Union at the EU level.