The XMLTutor is an Authoring Tool that generically delivers personalised teaching on an arbitrary domain, which must be specified in Extensible Markup Language (XML). The tool was built to explore the consequences of using XML to represent the domain ontological structure in an Intelligent Tutoring System (ITS). 1. Domain Knowledge Module Constructing domain knowledge can be a time intensive task . Often it is difficult for a domain expert to translate their knowledge and thinking into a foreign format. A promising solution to this difficulty is the XML format. XML has a natural hierarchical structure similar to the contents section of a book. This allows XML to store both structural and semantic information about the domain. Mizoguhi  describes this set of XML tags more formally as a kind of level 1 ontology. XML is used extensively outside the Intelligent Tutoring field as a data markup language and so many people would already be familiar with it. Furthermore, the language is very simple, making it an ideal format for non-computer experts to encode their factual knowledge in. The XMLTutor can read in an arbitrary XML file and deliver a personalised tutorial on the material inside it. There are already XML descriptions of almost everything from Stock Prices to Geography (see Figure 1). With little or no work, a tutorial can be constructed on any of these areas. <country name=”England”> <capital relevance=”5”>London</capital> <hemisphere relevance=”2”>north</hemisphere> </country> Figure 1. Example Domain Encoding The XMLTutor can do this because the knowledge is expressed in a common format. There is nothing 1 Procedural knowledge is better represented by a more powerful format, such as an expert system or programming language. immediately special about XML if this knowledge were encoded in a semantic network then the equivalent Semantic Network Tutor would be able to automatically generate tutorials as well. Having said that, there are real advantages to using XML for knowledge reuse over other possible formats. This paper will attempt to highlight some of these advantages.