This chapter analyses some key questions and dilemmas related to the involvement of national parliaments in mixed agreements. It focuses on bilaterally-structured mixed agreements (concluded by the EU and Member States on the one hand and a third party to the other) and not multilateral mixed agreements (where the EU, its Member States and usually many other states are all individual parties to the agreement). The chapter explores the legal and political reasons to opt for the mixed formula. It also analyses the role of the EP and the different national parliaments in the conclusion of mixed agreements. The chapter addresses three key legal questions or dilemmas related to national parliaments and mixed agreements i.e. is there a duty on the national parliaments to ratify? What exactly do national parliaments need to ratify? And what is their role with regard to the provisional application of such agreements?