IoTSyS is an integration middleware for the Internet of Things. It provides a communication stack for embedded devices based on IPv6, Web services, and OBIX to establish interoperable interfaces for smart objects. Using 6LoWPAN for constrained wireless networks and the Constrained Application Protocol together with Efficient XML Interchange, a powerful stack is provided in order to enable usage of interoperable Web technologies in the field of sensor and actuator networks and systems while efficiency regarding transmission message size remains nearly the same as in existing automation systems. The IoTSyS middleware aims at providing a gateway concept for existing sensor and actuator systems found in nowadays home and building automation systems (e.g. KNX, BACnet, ZigBee, or Wireless M-Bus) and a stack that can be deployed directly on embedded 6LoWPAN devices. Furthermore, it addresses security, discovery, and scalability issues.