This paper focuses on coordination middleware for distributed applications based on active documents and XML technologies. It introduces the main concepts underlying active documents and XML Then, the paper goes into details about the problem of defining a suitable middleware architecture to effectively support coordination activities in applications including active documents and mobile agents, by specifically focusing on the role played by XML technologies in that context. According to a simple taxonomy, the characteristics of several middleware systems are analyzed and evaluated. This analysis enables us to identify the advantages and the shortcoming of the different approaches, and to identify the basic requirements of a middleware for XML-centric applications.