This paper motivates and describes the notion of mobile ad hoc information systems. Such a system consists of a decentralized and self-organizing network of autonomous, mobile devices that interact as peers. Connectivity is determined by distance between devices; as hosts change their physical location they establish pair-wise communication links based on mutual proximity. We describe application scenarios for mobile ad hoc information systems and identify technical challenges of a generic software infrastructure. Moreover, we present the goals and architecture of Proem, a peer-to-peer system and development platform for mobile ad hoc applications. Proem has successfully been used as instructional tool in an advanced software engineering course on peer-to-peer computing.