This document provides a comprehensive model for the annotation and representation of referential phenomena in natural language texts and multimodal interactions. Such phenomena can cover simple anaphoric or coreferential mechanisms as well as more complex bridging or multimodal mechanisms. It provides a reference serialisation in XML defined as a customisation of the TEI P5 guidelines. In addition, the document describes the core data categories related to referential entities and link structures, and also needed for the description of annotation schemes and serialisation mechanisms for implementing conformant models as concrete data formats.