The first introductory chapter aims towards setting out a constitutional framework, a constitutional foundation upon which the following chapters of the thesis may be built upon. Setting out the foundational principles of the Union and Member State relationship is also a convenient starting point for the ensuing chapter concerning competence. The necessary treatment of external Union competence in chapter two provides for the discussion envisaged above concerning the scope for mixed agreements and the adjoining constitutional issue. For reasons of space and time, not all aspects of Union external competence will be considered. This thesis concentrates specifically upon the common commercial policy and what prior to the Lisbon Treaty constituted implied external Community competence. These areas have been frequently debated in the academic discourse and they have had and continue to have a considerable impact upon mixed agreements. The second part of the answer to why an evaluation of mixed agreements is needed is related to the use of the mixed agreement as such. As implied above already, difficulties with the management of the mixed formula constitute the most serious criticism of the mechanism. With no Treaty provision existing to do the job, the Court has developed the concept of the duty of cooperation as the tool to mitigate negative effects of Union and Member State cooperation. Unfortunately, as only abstract comments have been given in terms of its features, it remains unclear to what extent this duty of cooperation is being observed and what legal obligations are carried with it. Depressing conclusions of the collaboration between the Union and the Member States are by many taken for granted and advocates in favour of the use of pure Union agreements continue to occupy much of the discussion surrounding the mixed agreements. However, no greater exploration of the duty of cooperation and its function in relation to mixed agreements has of yet been undertaken. Accordingly, being the logical consequence of its first part, the management of the mixed formula constitute a fundamental part of this thesis. As already indicated, the dissection of the function of the mixed agreement also constitutes the necessary compliment to the constitutional issue advertised above.