In modern international law, it is a near consensus that no state can use force against another - the main exceptions being self-defense and actions mandated by a U.N. Security Council resolution. However, one more potential exception exists: forcible intervention undertaken upon the invitation or consent of a government, seeking assistance in confronting armed opposition groups within its territory. This dissertation seeks to analyze the consent-exception in a wide context, and attempting to delineate its limits - including, perhaps, cases in which government consent power is not only negated, but might be transferred to opposition groups.