The development of electronic commerce or electronic business systems (EC/EB systems) is subject to different conditions than the development of conventional software systems. Thus, software development processes which were employed for conventional systems until now must be adapted to these new conditions. EC/EB systems typically have a high degree of interaction, which makes factors like ergonomics, didactics and psychology especially important in the development of user interfaces. They typically also have a high degree of integration with existing software systems like legacy or groupware systems. The development of EC/EB systems requires a new software development process which takes the "time-to-market" factor into account and allos the reduction of development time while maintaining the same level of quality. This paper introduces and describes an adapted software development process for EC/EB systems and its special features using the development of an electronic commerce portal system as an example.