The thesis is result of research on user individual differences in using e-learning systems and on the effects of these differences on quality of user interaction and their learning achievements. The set of user individual characteristics which contribute to learning process and learning outcomes in adaptive education is identified. The results show that learning styles have the strongest influence on user interaction with adaptive learning systems. Review of existing systems employing adaptivity to learning styles reveals the potential for learning process to meet each individual student’s needs through adaptation of learning environments to students’ learning styles. Further research is conducted to identify adaptivity features at the lowest possible level of learning materials, i.e. learning concepts. The introductory chapter of the thesis brings motivation and objectives of the research. In the second chapter the field of adaptive education is presented and respective terminology is introduced. Adaptive learning management systems including Moodle LMS are described. The third chapter presents the state of the art in user individual differences in adaptive education. Systematic literature review is conducted and the taxonomy of 16 user individual characteristics that are used as efficient sources of adaptation is concluded. In the fourth chapter, Felder-Silverman model of learning styles is described and the review of existing systems adapting to learning styles is presented. The fifth chapter describes the development process of adaptivity model of an on-line course to learning styles of the users. The model is based on several theoretical and empirical determinantsAs a result, the model provides adaptivity guidelines and suggests concrete mechanisms for including adaptivity features into on-line courses structured as the series of web pages. The model is easily applicable into widely used educational systems such as learning management systems and other web-based systems that enable creation of courses composed of pages. According to the proposed model, adaptation to learning styles in respective courses is achieved at the level of pages and page fragments, which, according to the authors’ knowledge, make the model distinctive from existing approaches. In the sixth chapter, the implementation of the model into Moodle LMS is presented. An adaptivity module for Moodle, called Adaptivelesson is built as an extension of the Lesson module. Using Adaptivelesson module a teacher can create adaptive courses as a series of web pages organized into adaptive lessons. The outcomes of adaptivity mechanisms in terms of adaptive presentation are adaptive selection of pages, their order and mode of presentation. Adaptivity mechanisms for adaptive navigation support provide different levels of user control along with support for local and global orientation of the user along the course. The seventh chapter deals with evaluation of the proposed adaptivity model, i.e. the implementation of a prototype on-line course. Evaluation is considered in terms of usability and efficiency of the adaptive on-line course. Evaluation of efficiency, i.e. students learning achievements, is conducted as a controlled experiment with two experimental groups and a control group. The results did not confirm the hypothesis that learning in environment that is adapted to learning styles leads to higher learning achievements compared to learning in non-adaptive environment. For the purpose of usability evaluation of the model and respective on-line course, a novel evaluation approach is developed. To address the specificity of adaptive educational systems, the proposed methodology combines several usability approaches for technical and pedagogical usability assessment with the acknowledgement of the adaptive nature of online course. The results obtained by complementary methods of usability testing and heuristic evaluation show that implementation of proposed model enables pleasant learning experience. In addition, the results of usability evaluation provide guidelines for enhancing user interaction with the adaptive course. The research presented in the thesis reaches the expected contributions as follows. The first main contribution of the thesis is the taxonomy of user individual characteristics as sources of adaptation in adaptive learning systems. The taxonomy contributes to the body of knowledge on user individual differences and points to open issues and possible directions of further research in the field. The second main contribution of the thesis is the model of adaptation of on-line courses to learning styles of their users. Implementation of the model into an on-line course in Moodle increases the level of personalization of the course. At the same time, the effort of teacher who creates the adaptive course is decreased in comparison to the creation of non-adaptive courses. The third main contribution of the thesis is a novel approach to usability evaluation of adaptive learning systems. Proposed methodology enables to assess technical and pedagogical usability in specific context of adaptive learning process.