Advances in wireless technology and affordable info-appliances are making mobile computing a reality. Such appliances can both communicate with a fixed station or with other info-appliances in an ad-hoc manner. In both scenarios the transaction paradigm is vital to provide applications with consistent access to durable data. However, current mobile transactional systems fail to provide the so much needed adaptability to the large set of usage scenarios and applications semantics (e.g. disconnected work, relaxed ACID properties, etc.). We present a transactional object-based mobile system, called MobileTrans, that supports the definition and enforcement of transaction policies. Such policies are separated from the application code and specify transactions behavior: (1) how data is fetched, (2) how updates are performed, (3) the degrees of consistency and atomicity required. Transaction policies can be either declarative (e.g. XML) or programmatic (e.g. Java, C#).