These proceedings cover the lectures delivered at the Fourth International Summer College on Physics and Contemporary Needs held from June 16 - July 4, 1979 at Nathiagali, one of the scenic hill resorts in the northern part of Pakistan. The college was organised by Pakistan Atomic Energy Commission (PAEC) and co-sponsored by the International Centre for Theoretical Physics, Trieste (ICTP), Italy. It also received a financial grant from the University Grants Commi- ssion for the participation of physicists from various universities of Pakistan. The college was attended by 16 lecturers and invited seminar speakers. It was attended by 186 participants from 28 coun- tries and consisted of 15 concentrated days of lectures, seminars and informal discussions. These proceedings contain only regular lectures delivered at Nathiagali but the seminars held there are listed in the Appendix. This year the college put special emphasis on various energy systems, including their long term implications, and computer software. However, the lectures delivered at the college also covered a wide spectrum of physics. The series of the colleges of which the present college is the fourth one are an attempt to remove the barrier of isolation for the physicists working in developing coun- tries, far removed from active centres of research. Thus these colleges could help to fill the important gap in communication between the physicists of developing and advanced countries.