As it is known, there have been frequent and widely spread conflicts in African continent. Notably, as compared to other regions, East Africa has a focus of international attention for the last two decades that demand UN and other regional organizations intervention in a number of times. In connection with this crisis, both UN and AU (IGAD in some instance with AU) repeatedly declared their preparedness to cooperate for the maintenance of peace and security in the region. However, the modes of cooperation have never been very clear for long time. The UN Charter refers to regional organizations as a whole, without due regards to the specific challenges. Accordingly, it is very crucial to address these big challenges at a time when UN, AU and IGAD cooperation have become extremely necessary. Generally, this book will exposes the legal lacuna in reference to Chapter VIII of UN Charter in particular and the major challenges on the existing modes of cooperation – that proposed by Secretary General Boutros Boutros Gali, in general.