For some time, academics, politicians and officials within the European Union have been debating the Union's legitimacy. Broadly speaking, legitimacy concerns the (lack of) esteem in which citizens of the Union hold the Union’s laws, policies and institutions. In order to legitimate the Union, 'to bring Europe closer to its citizens', and to democratise the Union's law- and policy-making processes, so that ordinary Europeans will more willingly agree to further integration and more readily obey Union laws, transparency has been called for. This thesis first seeks to define transparency. If legitimacy is to be achieved by means of an increase in transparency, the concept of transparency must be multidimensional, including a right of the public to scrutinise and to participate indecision-making processes. Various claims concerning transparency-related issues are considered, including the claim that the right of public access to government- held documents is a fundamental human right. The thesis then asks whether the institutions and Member States are actively seeking to provide an appropriate level of transparency, and, if not, whether transparency as officially defined by the institutions and Member States - i.e. transparency as a right of public access to documents held by the institutions - is capable of providing legitimacy. The substantive rules governing public access to such documents are examined, and the thesis evaluates the effectiveness of the remedies available to persons to whom such access is denied. The creation of a new institution is recommended, to ensure the effectiveness of the Union's transparency policy, with a view to legitimating and democratising the Union. This new institution could facilitate a change in the Union’s culture, from a culture of secrecy to a culture of openness and willingness to permit public scrutiny of, and public participation within, the Union's decision-making processes.