The redox potential of an electron transfer protein is an essential property because it determines the driving force in an electron transfer reaction. The protein itself is an important determining factor since the redox potentials of analogs and proteins with the same metal site or of different proteins with the same metal site may differ by on the order of 1V. On the other hand, homologous proteins with the same redox site may have identical redox potentials or may differ by up to 500 mV, although the larger differences generally correspond to significant differences in the backbone fold. Different computational methods for understanding where these differences arise from will be discussed. Particular attention will be placed on how our knowledge of protein structure function relationships influences the techniques that are used. ©2000 American Institute of Physics.