This contribution discusses from a legal perspective the role of private actors for controlling compliance with public law greenhouse emission reduction obligations. Compliance is generally the Achilles heel of environmental law. Traditionally, the governments set standards and control compliance. Within the EU, however, the EU legislator is experimenting with involving self-control and verification procedures in view of determining compliance by industries with public law regulations. It does so by introducing in its regulation a mix of governmental and private action in view of effectively reducing greenhouse gas emissions. Moreover, in EU law, the public is given wide access to environmental information held by the government, which may also be beneficial, or at least to some extent helpful, for controlling compliance with set rules. In other words, civil society has some means to control governmental action, and, in this vein, the question arises to what extent these rules also apply to information held by the verifier. The contribution focuses on one specific but important case: it will discuss this regulatory mix of governmental and private action by delving into a key measure in EU climate law: the EU emissions trading scheme, thereby particularly investigating the role that private actors may play in checking compliance. In this respect, two categories of private actors will be distinguished: • On the one hand, the so-called verifiers that are tasked with controlling the emission reports of industries covered by the EU emissions trading scheme. In fact, the EU chose to apply a “double” market based approach: firstly, the industries are covered by emissions trading, and, secondly, the private sector (the verifiers) has to compete with each other for winning contracts with industries for conducting the control of the emission reports. • On the other hand, attention will be paid to the actors in civil society who want to check whether industries comply with EU law, in the sense of not emitting more than legally allowed. The role of civil society for strengthening (compliance with) environmental law, and hence contributing to the effectiveness of regulation, is stressed by the Aarhus Convention, giving important procedural rights like particularly the right to have access to environmental information held by the government. This procedural right may be helpful, to some extent, for checking compliant behaviour. However, how and to what extent can civil society check whether duties of industries with regard to controlling emissions are complied with? Can the private verifiers be covered by this access to information laws? In other words, can civil society use the procedural rights for checking the performance of the private verifiers? The ultimate aim of the contribution is to answer the question of how this (experimental) mix of governmental and private action for regulating the reduction of greenhouse gas emissions is designed in view of enabling transparency that is seen as a crucial element for reaching effectiveness: to what extent can civil society know about how industries are regulated and controlled, also in view of the fact that private actors (verifiers) have got the task to check compliance? This issue of transparency is chosen since, generally, public control (particularly action by Environmental NGOs) is seen as an effective tool to stimulate ambitious environmental regulatory action (although in this respect, also more research needs to be done on the effectiveness and legitimacy of ENGO action). The concluding section will summarize the findings by pointing at potential problems with transparency caused by the choice of using private actors for checking compliance with public standards.