Measurements of conduction electron spin resonance (CESR) in steel allow to separate the contributions from free electrons which provide the metallic character of interatomic bonds and from localized electrons involved in the covalent bonds. The data of the CESR study carried out on austenitic CrMn steels alloyed with carbon, nitrogen or carbon+nitrogen are presented. It is shown that, in contrast to carbon, nitrogen enhances the metallic character of atomic interactions with a maximum of the concentration of free electrons at some critical content of nitrogen (about 2 at.%). The combined alloying with carbon+nitrogen leads to two effects: (i) a larger concentration of free electrons and (ii) a shift of the critical content of interstitials towards higher values. The experimental data are supported by theoretical ab initio calculations of the electron properties of austenitic CrMn steels alloyed with carbon, nitrogen or carbon+nitrogen. Using the full-potentialfull- electron-linearized-augmented-plane-wave (FLAPW) method, the total energy per primitive crystal cell, the density of the electron states (DOS) and the distribution of the electron density over the crystal lattice were calculated by means of the computational program WIEN-2k. The total electron energy decreases due to alloying in the sequence of carbon→nitrogen→carbon+nitrogen, which suggests a corresponding increase in the thermodynamic stability of the austenite. The obtained results of the theoretical and experimental studies of the electron structure were used for the development of super-high–strength stainless austenitic steels.