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This is a study of the analysis of the concept of sustainable development. The linkages between environment and development, the meaning of sustainability and a critique of the decision making process are analysed through the comparison of two case studies the Aral Sea and the Billings reservoir. The rst study case is the Aral Sea. During the last thirty years the development of crop production was the goal of regional strategy of the Aral region countries. Wirhdrawls from the rivers caused inows to the Aral to fall at an average of over 50 km3 annually to 1-5 km3 in the 80´s. There have been observed accute environmental, health and social problems attributed to the development process. The Billings reservoir is located at the Southeastern region of the city of São Paulo, and was constructed in I937 with the objective of energy generation. During the years it was turned into a multiple-use reservoir including domestic and industrial water uses, as well as well as domestic and industrial deject reception. The accelerated development of the city and the lack of basic infrastructure projects such as sewage treatment have led to the advanced degradation of the reservoir. and to negative impacts and conicts for the entities and communities involved in the system. The study has shown that integration of environmental and developmental issues is very important for a balanced and efficient decisionmaking. This can be achieved through thorough studies of ervironmental, economic and social factors of the system under analysis. The meaning of sustainability has different dimensions for each system. Also a reformulation of the decisionmaking process is essential for the concept become operational.