The process of conceptual design is independent of the final platform and the medium of implementation, and is usually in a form that is understandable and usable by managers and other personnel who may not be familiar with the low-level implementation details, but have a major influence in the development process. Although a strong design phase is involved in most current application development processes (e.g., Entity Relationship design for relational databases), conceptual design for XML has not been explored significantly in literature or in practice. Most XML design processes start by directly marking up data in XML, and the metadata is typically designed at the time of encoding the documents. In this chapter, the reader is introduced to existing methodologies for modeling XML. A discussion is then presented comparing and contrasting their capabilities and deficiencies, and delineating the future trend in conceptual design for XML applications.