Environmental educators have to deal with a lack of interest in directly experiencing the natural environment and an increasing alienation from nature especially among younger generations. This thesis proposes a new concept for environmental education that should help to address these challenges by bridging the gap between computer-mediated environmental education approaches and the direct experience of nature. The new concept extends the traditional form of media-based environmental interpretation by means of a mobile context-aware computer system. This mobile nature guide system can assist its user during self-determined exploration and can dynamically adapt its presentation to the usage situation, preferences and current environmental conditions. The conceptual design specifies the components and services needed for a mobile nature guide, based on a comprehensive analysis of requirements and key environmental education instruments. Furthermore, an information technological concept is proposed along with a discussion of issues encountered during the implementation of a prototype system. In a field study the impact of the prototype mobile nature guide on environmental literacy and user satisfaction has been compared to that of traditional environmental education media.