The purpose of this study is to clarify the process of the construction of flexibility and plurality of identities by examining representation or interpretation of the cultural differences inside one ethnic group and between ethnic groups in the East African Pastoralists' Societies. Generally construction of self identity and construction of others are two sides of the same coin, and they thus proceed at the same time. In this study to clarify the logic people are using when they construct identities two main points are focused upon. Nakamura examined the cultural and social practices related to the age system among the Samburu people mainly focusing on the "moranhood" which is the age grade of unmarried male (moran) sometimes translated as "warriors." A regional difference between the general view of moranhood of highland and lowland of has become conspicuous. This difference makes both highlanders and lowlanders conscious of what they chose, and their identities as moran are defined differently. Naito examined the dynamics of the inter-ethnic antagonism and its practical solutions among the Rendille and Ariaal people in northern Kenya in relation to the decentralization and democratization of the Kenyan nation. The first clarifies the process of the construction of the different identities inside the ethnic group, and the second clarifies the process of the essentialization of the ethnic group over the political resources. In short, it is a process of reorganizing a group, within which many minute differences are contained, which becomes a monolithic and monotonous group.