The paper discusses the importance of the Technology Performance Levels (TPLs) as an essential metric for the assessment and quantification of the techno - economic performance at all stages of the wave energy converter (WEC) technology development and its significance to the successful deve lopment of economic technology. TPLs provide an integral technology assessment of all cost and performance drivers grouped into the five high level categories of acceptability , power conversion efficiency, availability , capital expenditure (CapEx) and lifecycle operational expenditure (OpEx), while broadly inversely related to cost of energy (CoE). Following previous introduction of the TPLs in [1], used alongside the Technology Readiness Levels (TRLs) in form of the TRL – TPL – Matrix visualisation providing a useful means for the evaluation, comparison and discussion of different research technology development trajectories over the technology readiness and performance levels plane, this paper recaps on the motivation for introduction and use of TPLs and extends their description through their fundamental principles. TPLs are applicable at all development stages over all TRLs and the associated techno - economical WEC technology assessments are described over a range of TPLs. The value of technology is discussed with respect to investability while under development and marketability when at product stage. It is shown that the combined consideration of both TRL and TPL are of the essence in order to a) identify requirements of WEC technology for successful entry and survival in the electricity market and b) assess actual value technology under development when crucial investment and funding decisions are made .