The newly founded European Centre of Excellence for Speech Synthesis (ECESS) is an initiative to promote the development of the European research area (ERA) in the field of Language Technology. ECESS focuses on the great challenge of high-quality speech synthesis which is of crucial importance for future spoken-language technologies. The main goals of ECESS are to achieve the critical mass needed to promote progress in TTS technology substantially, to integrate basic research know-how related to speech synthesis and to attract public and private funding. To this end, a common system architecture based on exchangeable modules supplied by the ECESS members is to be established. The XML-based interface that connects these modules is the topic of this paper.