Today multi-touch technology is the basis for many new techniques designed to improve interactions with computers and mobile devices. It seems that multi-touch screen interface makes the user handling very natural in the sense that there is no need for a manual in how to interact with the object on the screen. The aim with this paper is to establish a fundamental set of design principles intended specifically for large multi-touch interfaces. To reach this goal we have implemented a couple of sub-goals beforehand: It was essential that we acquired a good understanding of the current state of the multi-touch interface and the different implementations that exist today. To make this possible we constructed a multi-touch display, "Rosie". Knowing how the hardware is produced today will help us understand the limitations and also the possibilities of the design implementations today and in the future. We also needed to devise a sound interaction design process that conveys the modern designers work. During this design process four methods were implemented that gave us deeper understanding how to reach the result in this paper (design principles). The methods are: Qualitative conceptualisation, Qualitative user-testing, Participatory design, and Iterative prototyping. Doing these methods we gained knowledge through the process and experience of for example, building, running workshops, doing video-prototypes and etc. Creative design was very relevant in our design process. The result in this paper is a foundation for a set of design principles with relevance for multitouch interfaces and a interesting design process for developing multi-touch applications.