The 21st century started with the NATO intervention in Kosovo and continued with the "war against terrorism" in Afghanistan and Iraq. Both of these actions were resulted in the change of the governments of the countries in question. The very basics of the UN system are questioned with these actions. There is a growing amount of opposition to the actions of the United States. But again because of the veto system in the UN Security Council, the United Nations is not able to take action in international conflicts. The doctrine of humanitarian intervention might be the safety valve of the system when the UNSC is blocked by the veto power, but because of the fears of abuse of this mechanism could not be realised in the past. This book tries to focus topics like: The concept of State Sovereignty; can the use of force with this doctrine be justified by the violation of human rights? Is NATO’s intervention in Kosovo compatible with the criteria for humanitarian intervention? The way to deal with these topics was chosen to focus on the cases by examining how the doctrine and practice of humanitarian intervention evolved from past to present and the possible future practice.