Tidal energy is a very attractive renewable energy source due to its predictability. However, utility-scale implementation of tidal turbines and other types of tidal energy harvesting device has been slowed by the considerable investment costs required as well as the complexity of operation and maintenance of such systems. Pilot trials of various industrial-scale tidal turbine designs have revealed relatively low operational availability which in some occasions is below 25%. The operational availability of tidal energy devices needs to be increased substantially if they are to become commercially viable. Integrated condition monitoring (CM) can provide a reliable tool for assessing the in-service condition of critical components of tidal energy harvesting devices. The data produced by CM systems can enable cost-effective maintenance based on prediction rather than correction. This chapter presents the development of an integrated monitoring system for the continuous evaluation of the condition of critical rotating and structural components in tidal turbines. The system can be used to provide information regarding the presence of faults as well as advanced warning of impending failures. The system presented here has been based upon the detection of structural vibrations and Acoustic Emission (AE) responses, thus covering a wide operational frequency spectrum. A fatigue test bed has been designed and constructed to conduct impact tests on a mock-up of a tidal energy converter device and a second test rig has been developed to facilitate underwater testing on rotating components. The data analysis methodology for the evaluation of machine and structural faults detected during experiments on these test rigsare presented.