The rapid development of mobile technologies provides a great potential to support mobile work that was not supported by traditional stationary information systems. To realize this great potential, it is important for us to fully understand the nature of mobile work in order to develop efficient and effective support for mobile workers. In this paper we propose a conceptual framework and use this framework to analyze four fundamental aspects of mobile work: mobile workers, mobile tasks, mobile context, and mobile technology. The key differences between office work support and mobile work are highlighted. The conceptual framework can be used to identify research issues and provide guidelines for the development of effective mobile work support systems.