The software development has changed dramatically the last two decades. Software was primarily built in house 30 years ago, aiming to fit the needs of a specific user. During the 80’s the tendency changed with the foundation of software houses that were specializing in the development of “off the self” software, fitting the needs of a wider group of users, thus achieving scale economy, cheaper software with better quality. The last years, the explosion of the internet usage has transferred all applications to the “cloud” exploiting the faster and cheaper than ever hardware and netware. Furthermore, software systems such as Content Management Systems and Enterprise Resource Planning have transformed information system development into a process that connects the right components of functionality together. However, no matter what the advances are, tailored software is still required. Organizations, like businesses and institutions, with a variety in characteristics like delivered services, size, people, business processes and operating rules will always have a need for a customized system that fits their needs. Thus, building software has become more complex not in terms of available technological solutions but in terms of determining user needs. There are still excellent flawless software systems that solve the wrong problem. Therefore, enriching software engineering processes with business modeling techniques has been one way to cope with this problem. One of the most famous software engineering processes is the Rational Unified Process (RUP) which includes its own business modeling technique. In this thesis we try to combine DEMO and RUP in order to exploit the advantages of both methodologies which will ultimately assist practitioners in the development of quality software that solves the right problem. Our effort starts with the identification of a common scientific background, continues with devising a framework of assisting the combination and study of the methodologies. Then, the combined methodology is used in a case study in order to test in practice the new methodology.