|Abstract|| ||In this article we present Tuio, a simple yet versatile protocol designed specifically to meet the requirements of table-top tangible user interfaces. Inspired by the idea of interconnecting various existing table interfaces such as the reacTable*, being developed in Barcelona and the tDesk from Bielefeld, this protocol defines common properties of controller objects on the table surface as well as of finger and hand gestures performed by the user. Currently this protocol has been implemented within a fiducial marker-based computer vision engine developed for the reacTable* project. This fast and robust computer vision engine is based on the original d-touch concept, which is also included as an alternative to the newer fiducial tracking engine. The computer vision framework has been implemented on various standard platforms and can be extended with additional sensor components. We are currently working on the tracking of finger-tips for gestural control within the table interface. The Tuio protocol has been implemented using OpenSound Control and is therefore usable on any platform supporting this protocol. At the moment we have working implementations for Java, C++, PureData, Max/MSP, SuperCollider and Flash.