Determining the context of users and machines is an important topic in current computing research. An essential detail of a physical object?s context is its location, which includes both the actual position as well as the semantics of the surroundings. This paper focuses on the specific problem of determining the position of objects and people within buildings. A low-cost approach is based on wireless LANs, which are now widely deployed. The paper presents a sophisticated probabilistic algorithm for indoor positioning using wireless LANs, but also discusses the problems that need to be solved to make indoor geolocation commonplace.