Wind power installations have become the second largest contributor to installation of electricity capacity in the European Union during the last decade. With this increase in production capability and size, technical and economical efforts should be directed to achieving the optimal structural performance during the life cycle. The deterioration processes, such as fatigue and corrosion, are typically affecting offshore structural systems. This damage decreases the system performance and increases the risk of failure, thus not fulfilling the established safety criteria. Inspection and maintenance actions are the most relevant and effective means of control of deterioration. The risk-based inspection planning methodology, based on Bayesian decision theory, represents an important tool to identify the suitable strategy to inspect and control the deterioration in structures such as offshore wind turbines. During the last decades, Risk Based Inspection (RBI) approaches have been applied in the oil and gas industry, giving a theoretical background that can also be applied for offshore wind turbines. Unlike other offshore structures, offshore wind turbines represent low risk to society due to their offshore location, no pollution risks and low human risks since they are unmanned. This allows the allocation of lower reliability level compared to e.g. oil & gas installations. With the incursion to water depths between 20 and 50 meters, the use of jacket and tripod structures represents a feasible option that improves technical aspects concerning structural robustness, dynamical performance and damage distribution. Structural components such as support structures, transition nodes and towers, have critical design elements or zones that need special thorough design concerning fatigue damage. In this work, a framework for optimal risk-based inspection and maintenance planning for Offshore Wind Turbines (OWT) is developed. Fatigue prone details (in cast iron and welded steel) at the jacket or tripod steel support structures are addressed. For wind farms additional efforts are needed when wake are to be accounted for. Wake effects imply increased turbulence and thus decrease in OWT fatigue life and performance. In wind farm locations and single/alone locations of offshore wind turbines are considered, and probabilistic models for assessment of the fatigue reliability are developed. Further a reliability-based approach to calibrate Fatigue Design Factors (FDF) for offshore wind turbine support structures is described. The FDF values are calibrated to a specific minimum reliability level and a particular inspection and maintenance strategy. Generally, lower FDF values are obtained for offshore wind turbines than for oil & gas structures and reduced FDF values are obtained when inspections are taken into account. Thereby, the basis is available for selecting a cost-effective fatigue design for offshore wind turbines substructures. Additionally, the integration of condition monitoring information to optimize the damage-mitigation activities is considered. This work is contemplating the updating through Bayesian statistics and Monte Carlo Markov Chain techniques. The new information and uncertainty is incorporated with an orthogonal polynomial approximation for assessment of fatigue reliability. ; Wind power installations have become the second largest contributor to installation of electricity capacity in the European Union during the last decade. With this increase in production capability and size, technical and economical efforts should be directed to achieving the optimal structural performance during the life cycle. The deterioration processes, such as fatigue and corrosion, are typically affecting offshore structural systems. This damage decreases the system performance and increases the risk of failure, thus not fulfilling the established safety criteria. Inspection and maintenance actions are the most relevant and effective means of control of deterioration. The risk-based inspection planning methodology, based on Bayesian decision theory, represents an important tool to identify the suitable strategy to inspect and control the deterioration in structures such as offshore wind turbines. During the last decades, Risk Based Inspection (RBI) approaches have been applied in the oil and gas industry, giving a theoretical background that can also be applied for offshore wind turbines. Unlike other offshore structures, offshore wind turbines represent low risk to society due to their offshore location, no pollution risks and low human risks since they are unmanned. This allows the allocation of lower reliability level compared to e.g. oil & gas installations. With the incursion to water depths between 20 and 50 meters, the use of jacket and tripod structures represents a feasible option that improves technical aspects concerning structural robustness, dynamical performance and damage distribution. Structural components such as support structures, transition nodes and towers, have critical design elements or zones that need special thorough design concerning fatigue damage. In this work, a framework for optimal risk-based inspection and maintenance planning for Offshore Wind Turbines (OWT) is developed. Fatigue prone details (in cast iron and welded steel) at the jacket or tripod steel support structures are addressed. For wind farms additional efforts are needed when wake are to be accounted for. Wake effects imply increased turbulence and thus decrease in OWT fatigue life and performance. In wind farm locations and single/alone locations of offshore wind turbines are considered, and probabilistic models for assessment of the fatigue reliability are developed. Further a reliability-based approach to calibrate Fatigue Design Factors (FDF) for offshore wind turbine support structures is described. The FDF values are calibrated to a specific minimum reliability level and a particular inspection and maintenance strategy. Generally, lower FDF values are obtained for offshore wind turbines than for oil & gas structures and reduced FDF values are obtained when inspections are taken into account. Thereby, the basis is available for selecting a cost-effective fatigue design for offshore wind turbines substructures. Additionally, the integration of condition monitoring information to optimize the damage-mitigation activities is considered. This work is contemplating the updating through Bayesian statistics and Monte Carlo Markov Chain techniques. The new information and uncertainty is incorporated with an orthogonal polynomial approximation for assessment of fatigue reliability.