Wave energy converters (WECs) represent sophisticated engineering systems designed to transform the irregular, oscillatory motion of ocean waves into usable electrical power. This chapter examines the critical relationship between WEC device principles and their geometric design, highlighting how form directly influences functionality across diverse operational environments. By understanding the fundamental physical interactions between device geometry and wave hydrodynamics, engineers can develop more efficient, resilient, and economically viable wave energy solutions. The chapter is structured to provide comprehensive coverage across five interconnected sections. The fundamentals of WECs section establishes the core operating principles and classification systems, detailing energy extraction mechanisms, degrees of freedom, and power take-off approaches that determine overall system architecture. The geometry design principles section explores how specific geometric parameters—including scale, proportion, shape characteristics, and orientation—influence hydrodynamic response factors such as added mass, radiation damping, and resonance bandwidth, with dedicated analysis of geometric considerations for different WEC types. Optimization techniques in WEC geometry design presents advanced methodologies spanning from analytical approaches to sophisticated computational methods including high-fidelity CFD simulations, parametric optimization algorithms, and emerging machine learning applications that enable multi-objective design optimization across competing performance criteria. The case studies section provides detailed examples of geometry optimization in prominent WEC designs, demonstrating how theoretical principles translate into practical design decisions within specific operational contexts. The final section examines future trends in WEC design, including multi-functional structures serving purposes beyond energy generation, bio-inspired geometries leveraging evolutionary adaptations found in marine organisms, and adaptive morphing systems capable of reconfiguring to optimize performance across varying wave conditions.