This chapter addresses the critical role of Power Take-Off (PTO) control systems in maximizing energy extraction from ocean waves. The effectiveness of wave energy converters (WECs) depends significantly on how well their PTO systems can respond to the irregular and variable nature of ocean waves. PTO control represents one of the most promising pathways for improving WEC performance without substantial increases in capital costs, potentially reducing the levelized cost of energy (LCOE) for wave energy projects. Advanced control strategies enable WECs to adapt to changing sea states, optimize power capture across a broad frequency spectrum, and protect devices during extreme conditions, ultimately determining the commercial viability of wave energy technologies. The chapter begins with Sect. 5.1 which introduces fundamental concepts of PTO systems, including mechanical, hydraulic, pneumatic, and direct drive configurations, and their inherent control challenges. Section 5.2 explores methodologies for evaluating PTO control strategies, presenting analytical and numerical approaches for quantifying performance improvements under various wave conditions. Section 5.3 examines optimization techniques for PTO systems, covering both passive and active control methods, reactive control, and machine learning applications in real-time control systems. Section 5.4 provides detailed case studies of PTO control implementation in operational wave energy projects, offering practical insights into successes and challenges in real-world applications. Finally, Sect. 5.5 investigates emerging trends in PTO control technology, including predictive control algorithms, distributed control architectures, and integration with energy storage systems to enhance grid compatibility.