Today's interactive television systems are using proprietary communication protocols and interchange formats. To provide inter-operability at the application level the next generation of interactive television system will be based on standardized communication protocols, monomedia and multimedia formats. This paper presents the Globally Accessible Services (GLASS) system which is a prototype interactive television system based on the Multimedia and Hypermedia Expert Group (MHEG) standard. After a brief introduction to MHEG as the multimedia interchange format between application server and set-top box in interactive television systems, the GLASS clients and servers are described, and an example scenario for navigation in the GLASS system is provided.