Successful development of economical wave energy converter (WEC) systems requires an integrated and balanced research technology development process and a thorough understanding of the economic performance criteria over the system lifecycle. Core performance attributes are associated with WEC concept, technology, operation and wavefarm economics and include survivability, power output, availability and cost. Both integrated system optimisation and successful research technology development routes require appropriate WEC system assessment tools. The paper describes the structure of an integrated techno-economic WEC system performance assessment framework. This comprises a WEC engineering analysis and a wavefarm lifecycle analysis. Both are presented in content and structure. Six core sub-models of the wavefarm lifecycle analysis are described and generic example results are provided. It is shown how the WEC system performance assessment framework provides a solid foundation for implementation of an integrated techno-economic WEC system optimisation. Finally, the importance of the assessment framework for identifying shortcomings in the development programme and in achieving an objective, efficient and successful research technology development process is discussed.