In a very short time, Sweden decided to change its military non-aligned security and defence policy to a policy as an allied member of NATO. This project studies the constitutional and international law dimensions of the policy change. The Swedish constitution - the Instrument of Government - regulates the balance of power between government and parliament in the field of defense policy. How decisions are made to give and receive military aid is regulated by the Instrument of Government. One question that arises is what role the Riksdag plays in the decision. Another question is what and how much power Sweden can transfer to foreign countries and organizations. The EU Treaty includes a common security and defense policy, including a mutual defense clause, which will now be implemented in a new NATO context. The legal implications of the rapid transition from non-aligned to allied may have been underestimated.