The exploitation of ocean wave energy as a renewable energy source is a challenging task. However, once economically viable, wave energy can make a significant contribution to the global renewable energy mix and, thereby, aid the fight against climate change. To support this action, researchers and developers devise and optimise wave energy converters, employing complementary analysis in physical and numerical wave tanks, as well as during open ocean trials. Compared to physical wave tanks, numerical wave tanks provide an excellent numerical test–bed, allowing the investigation of different device designs and scales, with the ability to passively measure relevant variables at arbitrary locations throughout the numerical domain. Generally, numerical wave tanks can achieve different levels of fidelity, at different levels of computational cost. At the lower end of the fidelity spectrum, numerical wave tanks based on linear potential flow theory assume linear conditions (small wave amplitudes and body motions) and are computationally efficient tools for, e.g., early stage design. However, the linear assumptions are pushed beyond the limits of validity when large body motions or non–linear free surface deformations occur. In contrast, at the upper end of the fidelity spectrum, numerical wave tanks based on computational fluid dynamics can capture all relevant hydrodynamic non–linearities and produce high resolution data sets, but require substantially more computational resources. Reviewing the available literature of high–fidelity numerical modelling of wave energy converters, knowledge gaps can be identified, hampering the exploitation of the fidelity of the computational fluids dynamics framework. Focusing on high–fidelity numerical modelling of wave energy converters, this thesis aims to fill some of the identified gaps. In particular, this thesis investigates the aspects of numerical wave generation and absorption, model validation, dynamic mesh motion methods, the flow field around devices, scaling effects, and the assessment of energy maximising controllers for wave energy converters within computational fluid dynamics based numerical wave tanks. Ultimately, this thesis highlights the potential of high–fidelity numerical models of wave energy converters to support device development, but also shows the complexity of this modelling framework. With the additional knowledge, gained through the work presented in this thesis, steps towards truly high–fidelity, wave–to–wire, models of wave energy converters can be taken to push devices towards commercial viability and, ultimately, transform wave energy from an untapped energy source to a significant contributor to the global renewable energy mix.