Metalloprotein electronics shares with molecular electronics the bottom-up approach to the assembly of devices, as well as the use of intrinsically functional units. The intrinsic functionality present and demonstrated in each metalloprotein suggests the charming implementation of single-molecule devices, which requires a number of technological and biophysical problems be solved. The efficiency with which redox metalloproteins perform the task of transferring electrons, along with their intrinsic nanometer size, optimized by natural evolution along billions of years, makes them ideally suitable candidates for technological aims, namely for implementing bioelectronic devices. Metalloproteins that function solely in electron transfer reactions possess metal centers that undergo minimal changes upon varying their oxidation state. Among the electron transfer metalloproteins, an important family is that of the so-called blue copper proteins. The genesis of the nowadays approach to biological electron transfer reactions dates back to the late 1940s, when coordination compounds with radio-labeled transition metals were used to study inorganic electron transfer reactions.