Koleva, BorianaBenford, SteveGreenhalgh, Chris2017-04-152017-04-151999978-0-306-47316-6Mixed reality boundaries establish transparent windows between physical and virtual spaces. We introduce a set of properties that allow such boundaries to be configured to support different styles of co-operative activity. These properties are grouped into three categories: permeability (properties of visibility, audibility and solidity); situation (properties of location, alignment, mobility and segmentation); and dynamics (properties of lifetime and configurability). We discuss how each of these properties can be technically realised. We also introduce the meta-properties of symmetry and representation. We then describe and compare two contrasting demonstrations, a performance and an office-door, that rely on different property configurations.enText10.1007/0-306-47316-X_7