This proceedings volume contains 33 papers presented at the 3rd Working Conference on "Rel- iability and Optimization of Structural Systems", held at the University of California, Berkeley, California, USA, March 26 -28, 1990. The Working Conference was organised by the IFIP (Inter- national Federation for Information Processing) Working Group 7.5 of Technical Committee 7 and was the third in a series, following similar conferences held at the University of Aalborg, Denmark, May 1987 and at the Imperial College, London, UK, September 1988. The Working Conference was attended by 48 participants from 12 countries. The objectives of Working Group 7.5 are: * to promote modern structural systems optimization and reliability theory, * to advance international cooperation in the field of structural system optimization and reliability theory, * to stimulate research, development and application of structural system optimization and reli- ability theory, * to further the dissemination and exchange of information on reliability and optimization of structural systems * to encourage education in structural system optimization and reliability theory. At present the members of the Working Group are: A. H.-S. Ang, U.S.A. G. A ugusti, Italy M. J. Baker, United Kingdom P. Bjerager, Norway R. B. Corotis, U.S.A. C. A. Cornell, U.S.A. M. Grigoriu, U.S.A. A. Der Kiureghian, U.S.A. O. Ditlevsen, Denmark D. M. Frangopol, U.S.A. S. Garribba, Italy H. Furuta, Japan M. R. Gorman, U.S.A. M. Grimmelt, Germany, F. R.