Presented in this section, these are few selected examples of wired and wireless condition monitoring systems (CMS) for wind turbines (WTs) developed and tested all over the world in the past decade. There are literally dozens of the systems, which are still in the process of testing in the field and installation on wind farms. The principles of these systems are based on multiple modern techniques, which are very effective in determining damage in all components of WT including its structure. Use of such systems is very important in providing educated base for condition-based maintenance (CBM) and life extension of WTs.