Reliability-Based Optimization (RBO) for engineering design deals mainly with two design attributes, the cost and the reliability of the design. The reliability considerations are typically driven by the probabilities of failure due to component failure events or a system failure event. These failures can be estimated using standard reliability analysis techniques such as First Order Reliability Method (FORM), Second Order Reliability Methods (SORM) and Monte Carlo Simulation (MCS) techniques. This book presents research work pertaining to two areas - one related to development of efficient approaches and improved reliability analysis techniques that reduce computational complexity and increase the success of using FORM in RBO of multidisciplinary systems, and second related to applying improved reliability techniques such as conditional expectation MCS combined with system reliability concepts.