This chapter deals with a discussion of wind turbine operations and maintenance (O&M), which is in and of itself an important part of reliability management. Wind turbine O&M plays an important role and accounts for a major portion in the total cost of energy in wind power production. The concept of condition-based maintenance is to collect the online monitoring data, and upon diagnosing a turbine’s condition, decide whether and when maintenances are needed. The challenges in wind turbine maintenance are primarily caused by the stochastic nature of turbine operation conditions and the uncertainties in the decision variables induced by the stochasticity. The sheer size of wind turbine components makes it difficult to store spare parts in a warehouse waiting for repairs or replacements. The methods of wind turbine maintenance commence rather naturally with analyzing the historical failure data to elucidate a component’s failure probability and then plan maintenance accordingly.