Designing information systems is a complex task. The purpose of this work is to contribute to an improved understanding of the design conditions in order to alleviate the problems that occur due to complexity in the design process. To possibly increase the understanding of the conditions for the design of interactive information systems, this dissertation concerns applying systems approach to the design situation. This is done in order to obtain understanding, but also to be able to identify the consequences and possible benefits of doing so. A literature survey and two extensive interviews have been performed. The material has been analysed, and tentative models of the design situation and its components are presented. These models can be considered general to the design situation and consequences are deduced from them. The result of this work is manifested in the tentative models, which describe the design situation, the designer, the user, the customer and the design. The concepts of complexity and communication have also been thoroughly dealt with.