Does a government always have the right to invite foreign troops to help it, even if the government is undemocratic, has no control over its territory and there is civil war in the country? Should a government have such an unconditional right? If a state is subject to a terrorist attack by a non-state group, does a right of self-defense arise for the state against the terrorist group? If so, which is currently the most common answer internationally, does the state have the right to retaliate militarily against the terrorist organization on the territory of a foreign country even if the foreign country cannot be held responsible for the attack? Should the attacked state have such a right? What rules of international humanitarian law, including human rights, are applicable to troops participating in a multinational military operation in an armed conflict? The rules (if any) that bind the organization leading the operation; the rules that bind the state leading the operation; or the rules by which the home state is bound? Which legal situation should prevail? These questions are examined in the light of Swedish experiences and positions. The starting point is Sweden's contribution to the US-led Operation Inherent Resolve in Iraq in 2014, Sweden's contribution to the UN-supported and NATO-led Resolute Support Mission in Afghanistan in 2015, the Swedish response to the terrorist attack in Paris in 2015, and the participation of Swedish troops in the UN-mandated and NATO-led International Security and Assistance Force in Afghanistan 2002-2014.