Proactivity has recently arisen as one of the focus areas within HCI. Proactive systems adhere to two premises: 1) working on behalf of, or pro, the user, and 2) acting on their own initiative. To extend researchers’ views on how proactive systems can support the user, we clarify the concept of proactivity and suggest a typology that distinguishes between 6 modes of proactive resource management: preparation, optimization, advising, manipulation, inhibition, and finalization of user’s resources. A scenario of mobile imaging is presented to illustrate how the typology can support the innovation of new use purposes. We argue that conceptual developments like the one proposed here are crucial for the advancement of the emerging field. Author Keywords Proactivity, proactive computing, ubiquitous computing, context, user-centered design. ACM Classification Keywords H5.2. User Interfaces: Theory and methods.