This dissertation concerns armed intervention by invitation in international law. In its essence, intervention by invitation entails the use of force with the consent of the territorial State, which appears simple. However, the modern form of the concept is fraught with legal complexities, including its relationship with the United Nations Charter. The instrument, which should regulate the use of force and make it a collective matter, does not mention unilateral intervention by invitation, leaving its legal basis complicated. Still, this impasse has been bypassed, allowing the concept to exist despite its inherent contradictions.