This doctorate thesis is an exploratory study of distributed and computer-mediated collaborative learning. The work lies in the intersection of the research domains: Computer Support for Collaborative Learning (CSCL) and distance education. The notion of Computer Support for distributed Collaborative Learning (CSdCL) is introduced in this thesis to focus on collaborative learning situations where the students are individually separated by physical distance. The thesis presents and discusses findings from my investigations on a number of CSdCL cases. Based on these investigations I argue that the students' collaborative processes are affected by various factors. These factors manifest themselves in a field of tension between existing institutional practice on learning and teaching, physical separation of the collaborating students, and computer systems that serve as mediators of collaboration. To what extent this field of tension is critical to the students' collaborative processes and to individual outcome of collaborating, is dependent on subject matters and pedagogical principles prescribed in the pedagogical method. I argue, however, that existing practice and methods must be reconsidered for CSdCL purposes. Concerning systems design, I argue that heterogeneous computer environments and networked computers must be taken seriously to make computer systems that work as resources for distributed collaborative learning. Based on this argumentation, I have developed two frameworks that are aimed at guiding an institution's planning of CSdCL and computer systems design, respectively. The first framework focuses on issues that treat CSdCL differently from more conventional forms of learning and teaching. The second framework focuses on tensions between computer systems and central principles of collaborative learning. I have used the frameworks in a practical design situation. The CSdCL designs were based on the pedagogical ideals of project-based learning and on the opportunities that World Wide Web gives to communication across a wide range of platforms. The results are a pedagogical approach to CSdCL and a computer system. I conclude, however, that it is still complicated to develop solutions for CSdCL that result in good practice. Good practice is not only dependent on good design ideas but also on organizational as well as individual maturity with respect to using new technology in learning. Today, CSdCL is just in the beginning of a path to such a practice.