The Evueví (commonly known as the “Payaguá”), a Guaycuruan tribe in southern South America, dominated the Paraguay and Paraná rivers for more than three centuries. Non-sedentary, similar in nature to the Chichimecas of northern Mexico and the Araucanians of southern Chile, the Evueví were riverine Indians whose life was seriously disrupted by the westward expansion of the Spanish and Portuguese in the Gran Chaco and Mato Grosso regions. This study will identify Evueví strategies for survival and analyze the nature of intercultural contact between the Indian and Spanish cultures. A study of the ethnohistory of the Evueví contributes to an understanding of the cultural adaptation of a non-sedentary indigenous tribe on the Spanish frontier whose salient features were prolonged Indian wars, Indian slavery, and missions. Such an analysis also provides an opportunity to analyze European attitudes and perceptions of a South American indigenous culture. Unlike other Amerindians, the unique characteristic of the Evueví was that Europeans perceived them as river pirates during the colonial era.