Recent years have seen widespread adoption of the Internet for language teaching and learning. Interactive systems on the World-Wide Web provide useful alternatives to face-to-face tuition, and both teachers and learners can benefit from the exercises available. However, although there is a wealth of suitable material, it is hard to find because it is scattered around the web. Moreover, teachers are restricted by the material that is available, and cannot provide their own. To tackle these problems we have constructed a digital library of language learning exercises that presents students with different kinds of exercise, and also lets teachers contribute new material. We first reviewed existing language learning systems on the web in order to develop a taxonomy of exercise types used for language activity. A prototype, ELLE, based on this taxonomy, provides various kinds of interactive exercises using material that teachers submit. The system has been evaluated by practicing language teachers.