The assessment of performance for PEM Fuel Cells (PEMFC) at the stack, Single Repeating Unit (SRU), and Membrane Electrode Assembly (MEA) level is dominated by the evaluation of polarization curves. However, polarization curves do not provide adequate detail as to the origin of the inefficiencies of the fuel cell performance and information on these sources of origin are critical to understand and address topics such as material selection, optimal operating conditions, and overall robust and reliable cell and stack design characteristics. To the purpose of understanding the origin of the inefficiencies underlying the fuel cell polarization curve a series of additional experimental and analysis techniques must be applied and from the resultant data the origin of the inefficiencies can then be assigned to kinetic, ohmic, and mass transport loss categorizations. Further, through a combination of the diagnostic methods further resolution can be implied down to the contribution of the individual components to the relative voltage loss categories. In this topic, a methodology will be presented and discussed that achieves and demonstrates this process.