This chapter discusses the reliability, operation and maintenance strategies for wind power systems. It examines the role of systems engineering in optimising the aspects of a system relating to reliability, supportability and maintainability. It considers various maintenance approaches and the role of proper maintenance practices in providing a secure and reliable energy supply at the right cost. It discusses the importance of identifying and understanding the relevant cost factors associated with wind power systems, based on lifecycle costing and using relevant performance measures to help select a cost-effective maintenance approach. It then reviews some efforts aimed at improving the design, production, construction, operation and maintenance of wind power systems. Finally, some future trends are discussed in the areas of operation and maintenance of wind power systems.