The proper functioning of the EU financial market is protected by public actors - both national and supranational - responsible for rulemaking and supervision of investment firms and other private actors. At the same time the effectiveness of the EU legal system requires vigilance from private actors such as investment firms but also their clients, invoking their rights before national authorities and courts. This means that investment firms have a dual role within the system, turning them into subjects of control and enforcement but also agents in the maintenance of the rule of law. Legal Accountability in EU Markets for Financial Instruments brings together a group of scholars with expertise from different legal disciplines but a shared interest for the EU internal market and the way it develops. It integrates a modern study of the form and function of EU rulemaking in the internal market after the financial crisis. The book includes an evaluation of core aspects of rulemaking in the financial market and that way provides a cross-cutting treatment of EU law. The focus of the book is set on the regulatory framework in MiFIDII and MiFIR and thematic questions around legal mechanisms for accountability and the role of investment firms in the operation of those mechanisms. It further discusses the implications for EU law and the EU legal system and gives readers a thorough understanding of the concept of accountability through its own findings.