Cytochrome c oxidase (CcO) catalyzes the four electron reduction of molecular oxygen to water while avoiding the formation of toxic peroxide; a quality that is of high relevance for the development of oxygen-reducing catalysts. Resonance Raman spectroscopy has been used since many years as a technique to identify electron transfer pathways in cytochrome c oxidase and to identify the key intermediates in the catalytic cycle. This information can be compared to artificial systems such as modified heme-copper enzymes, molecular heme-copper catalysts or CcO/electrode complexes in order to shed light into the reaction mechanism of these non-natural systems. Understanding the structural commonalities and differences of CcO with its non-natural analogs is of great value for designing efficient oxygen-reducing catalysts. In this review therefore Raman spectroscopic measurements on artificial heme-copper enzymes and model complexes are summarized and compared to the natural enzyme cytochrome c oxidase. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.