Mobile devices have become an intrinsic part of people's everyday life. They are multifunctional devices providing ubiquitous access to many different sources of information. Together with traditional personal computers, these devices form a device ecology that provides access to an overlapping information space. Previous studies have shown that users encounter a number of fundamental problems when interacting with these device ecologies, such as lack of transparency, control, intelligibility and context. To mitigate these problems, we introduce ActivitySpace: an activity-centric configuration space that enables the user to integrate and work across several devices by utilizing the space between the devices. This paper presents the conceptual background and design of ActivitySpace and reports on a study with nine participants. Our study shows that ActivitySpace helps users to easily man-age devices and their allocated resources while also exposing a number of usage patterns.