When attempting to get a software product to reach a larger part of the market, portability is a key factor. Unfortunately, it is often neglected from the software development cycle, and rather achieved by ad hoc methods in not very cost-effective ways. This thesis investigates portability in the context of mobile development. Previous research in this particular area has been hard to find, despite there obviously being special aspects surrounding it which are worth investigating further. The project was initiated with a literature study to find out the current state-of-the-art for portability. After this step the development of a mobile application was conducted, before which a market analysis had been carried out in order to explore which mobile platforms would be the most relevant to develop it for. The point of this case study was to attempt to achieve as high a degree of portability as possible, to later port the application to another platform. Based on the data gathered from this, conclusions were drawn and a general model with guidelines for developing mobile applications with portability as a main attribute was constructed. Among the more important lessons learned was that portability is more important in mobile development, due to the market being so diverse, while it also is a lot harder to achieve properly. This research will hopefully help development teams see the strengths and weaknesses of mobile application portability more clearly, allowing them to more easily design for it as well as making it a more intricate part of their process.