The yeast cytochrome c peroxidase (CCP)–cytochrome c (cytc) electron transfer system has been critically important in deciphering the molecular level details of protein–protein interactions and electron transfer. The crystal structure of the CCP–cytc together with a number mutagenesis, enzymological, and spectroscopic studies have provided a detailed picture on the overall mechanism and has led to a deeper understanding of how oxidizing equivalents are stored and stabilized in metalloproteins. More recently, a second CCP-like enzyme, Leishmania major peroxidase (LmP), has been characterized. The LmP–cytc structure is very similar to the yeast CCP–cytc structure with respect to the active docking surface although the LmP–cytc complex is dominated by electrostatic interactions while the yeast system relies more heavily on nonpolar interactions. In addition, the LmP system exhibits simpler enzyme kinetics and more straightforward ionic strength dependence, which offers some advantages in correlating kinetic studies with mutagenesis and other biophysical approaches.