First, the development history of a common foreign and security policy in Europe is presented, along with a detailed account of the contractual and non-contractual evolution of the EU's security and defense policy. Then, the regulations for differentiated integration in the area of the European Security and Defense Policy (ESVP), including their implementation provisions in the operational part of the Constitution for Europe, are outlined, as well as the provisions related to security and defense policy. The enhanced and permanent structured cooperation among some member states of the Union, as well as the military assistance clause, are discussed in detail and legally analyzed, drawing comparisons to the currently applicable provisions of the Treaty of Nice and highlighting differences, significant changes, and any improvements of the constitutional treaty.