This thesis proposes a new genre of outdoor games for children, namely Head Up Games. The concept was inspired by the observation that existing pervasive outdoor games for children were mostly played head down, as the predominantly screen-based interaction of existing games required constant attention of the children. First, the vision of Head Up Games is described and illustrated with several design cases (Chapter 2). In contrast to the head down games, Head Up Games aim to encourage and support rich social interaction and physical activity, play behaviors that are similar to play behaviors seen in traditional outdoor games (such as tag and hide-and-seek). The design process of Head Up Games poses several challenges. In User Centered Design it is commonly accepted to start the development of a new product using low-fi mock-ups, e.g., paper prototypes, and evaluate these with end-users. In the case of Head Up Games this proved to be difficult, as the emerging game experience is significantly altered when using paper prototypes. Therefore, a study was carried out that used high-fi prototypes, i.e. working, interactive, prototypes, from a very early stage in the design process (Chapter 3). This way, the effect of interactions on the game experience can be addressed earlier and better in the design process. Furthemore, having access to technology early in the design process, allows designers to better explore the design space. However, designers often do not possess adequate skills to quickly prototype interactive products, particularly products that need to be evaluated in an outdoor context. Such a development is often costly and time-consuming. Therefore, the RaPIDO platform was developed (Chapter 4). The platform not only includes the appropriate hardware for creating outdoor games, but is also bundled with software libraries, to allow designers not specifically trained in software engineering to adopt the platform easily. RaPIDO was evaluated using a case study methodology with two Industrial Design master students. The evaluation not only focused on the usability of the platform, but, more importantly, how the use of the platform affected the design process. The main conclusion of the study was that the designers indeed were able to rapidly create mobile games, and that the hardware offered was suitable for creating outdoor games. Furthermore, issues were identified with regard to writing the game software, e.g., managing the complexity of the software. Finally, for evaluating Head Up Games with children two methods were applied: the Outdoor Play Observation Scheme (OPOS) was used to quantify the intended play behavior. Furthermore, GroupSorter was developed to provide a framework to interview a group of children simultaneously, resulting in qualitative comments. Both OPOS and GroupSorter were applied for evaluating three Head Up Games, which are described in Chapter 5
