Recently, there has been increasing recognition that computer-based information systems should better support corporate sustainability management. New administrative approaches, e.g. in the field of emission trading, and recommendations, for instance regarding carbon footprints of products, require a new type of information systems in companies. These new components can be called corporate environmental management information systems (CEMIS). What is the purpose of these systems? They should provide the required information for environmental or sustainability management. But what is the idea behind? What is the guiding principle of these systems? This chapter discusses efficiency as a guiding principle of CEMIS. It helps to understand better basic methodologies like life cycle assessment, and it provides presuppositional knowledge for the challenge of introducing these information instruments