The University of Oxford has thirty-nine colleges, and five permanent private halls (PPHs) of religious foundation. Colleges and PPHs are autonomous self-governing corporations within the university. These colleges are not only houses of residence, but have substantial responsibility for teaching undergraduate students. Generally tutorials (one of the main methods of teaching in Oxford) and classes are the responsibility of colleges, while lectures, examinations, laboratories, and the central library are run by the university. Students normally have most of their tutorials in their own college, but often have a couple of modules taught at other colleges or even at faculties and departments. Most colleges take both graduates and undergraduates, but several are for graduates only.