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...