These proceedings cover the lectures delivered at the Third International Summer College on Physics and Contemporary Needs held from June 17 - July 5, 1978 at Nathiagali, one of the scenic hill resorts in the northern part of Pakistan. The college was organized by The Pakistan Atomic Energy Commission (PAEC) and co-sponsored by the International Centre for Theoretical Physics, Trieste (ICTP). It also received a financial grant by the University Grants Commission for the participation of physicists from various universities of Pakistan. The college was attended by 14 lecturers, 2 invited seminar speakers and 156 participants from 23 countries and consisted of 15 concen­ trated days of lectures, seminars and informal discussions. These proceedings contain only regular lectures delivered there, but the seminars which were held there are listed in the Appendix. This year the college put special emphasis on energy, parti­ cularly on nuclear energy and its role in the context of energy sys­ tems. However the lectures delivered at the college also covered a wide spectrum of physics. The lectures gave an overview of various topics covered at the college and emphasized the inter-disciplinary aspects of physics. Some of the lecturers also indicated the areas where research in developing countries with limited facilities could be carried out. The college had a definite objective of encouraging the physicists, part~cularly those working at the universities, to apply their knowledge of physics and methodology of research to the needs of modern society.