Semantic technologies provide for the expression of meaning of resources such as content, software, systems, people, and communities in machine processable formats with the help of ontologies. Ontologies provide the vocabulary for describing resources and their relationships (Gruber 1993; Musen 1992). Based on the meaning of resources, semantic technologies can draw conclusions and enable better resource discovery and matching. In a learning context, the potential of semantic technologies translates to a number of affordances. Thetypes of resources involved in formal or informal learning environments could include learners, teachers, software, services and content. Given the description (or annotation) of these resources with the help of ontologies, it is possible to support more efficient discovery of learning resources, sequencing of relevant learning material, adaptation of learning experiences to match learner profiles, formation of groups for teaching learning activities, collaborative construction of knowledge, recommendation of learning resources and activities, and assessment. A number of ontologies are developed in the learning domain in order to support these applications with the help of reasoning software.