The areas of Probabilistic Risk Assessment (PRA) and reliability engineering have seen significant developments in theoretical conceptualization, mathematical and computational modeling, and cross-discipline and cross-domain learning. Engineers and mathematicians from across disciplines have contributed to and have benefited from these developments. Nevertheless, current building and/or structural codes, as well as engineering design principles, do not fully incorporate PRA principles and methods. However, in situations where state-of-the-art or emerging methods have been used, PRA approaches have already demonstrated their value. This chapter discusses state-of-the-art and emerging methods and principles in reliability and risk-based engineering with examples.