Building structure­ to­ property relationships is one of the most often attempted research tasks in today's chemistry of materials. Often relationships are directly dependent and easy to identify. In complex, nano­ structured functional materials, those correlations are intertwined and multi­directional. Predicting macroscopic property of interest, such as activity, wettability, stability, etc., based on correlation with materials surface chemistry is challenging but yet accomplishable. The relationship between functional property and the chemical structure of materials is typically established through correlations between performance metrics parameters and various spectroscopic techniques, including XPS, XANES, XPES, TOF­SIMS, and Mössbauer spectroscopy. The primary advantage of XPS in the characterization of heterogeneous multicomponent nanostructures is the ability to discriminate between different surface oxidation states and chemical environments. However, the assignment of XPS peaks in highly heterogeneous materials is not straightforward. A significant improvement in the assignment of peaks at various binding energies could be achieved using reference materials, yet, many relevant reference materials do not exist. State­of­the­art computations allow the determination of BE shifts for specific defect chemistries and geometries, providing valuable information for processing and interpretation of spectra data. In this talk, I will discuss approaches towards structure­to­property relationships derived for energy­ related materials, such as electrocatalysts for fuel cell and biocatalysts for microbial fuel cells. I will discuss multivariate approaches towards correlating XPS data with performance characteristics and binding energy shift calculations using DFT for interpreting XPS spectra. Application of XPS instrumentation with in­situ capabilities to study materials under conditions relevant to their application will be also discussed.