There are now many CALL authoring packages that can create interactive websites and a large number of language teachers are writing materials for the whole range of such packages. Currently, each product stores its data in different formats thus hindering interoperability, pooling of digital resources and moving between software packages based in different technology. The use of Extensible Mark-up Language (XML) for data storage goes a long way to solve this problem and allows for the easy conversion of exercises. Starting from a desire to develop a common format between "Hot Potatoes, WELTS" (part of the WELL project) and the "Interactive Language Learning" package from London Metropolitan University, a new version of the "Interactive Language Learning" software, now renamed Guildhall Interactive Software for Multimedia On-line (GISMO), has made such conversion possible. Given the immense resources required to develop the critical mass of material required to make online CALL relevant to an individual's teaching practice, such a common approach is required to facilitate the pooling of resources. Should a bureaucratic or financial decision in an institution result in a change of software, teachers need to be able to easily convert their legacy material. XML technology can facilitate interoperability, thereby increasing potential accessibility by allowing teachers and students to have the use of a greater amount of pedagogical material. It is further proposed, using these developments, to create a large pool of exercises for practice and assessment that is independent of the delivery approach employed. This will obviate the need for teachers to keep reproducing basic language learning material and allow for the expansion of online CALL into more imaginative areas. This possibility introduces the question of standards within XML and whether it is necessary to further specify how the material is stored, perhaps using a standard such as the "IMS Question & Test Interoperability Specification" or whether XML is a sufficient standard in itself.