We have investigated the electrical, optical and mechanical properties of CrN y and Cr 1 - x Si x N 1 . 0 2 films as a function of N and Si contents near the fcc-CrN stoichiometric composition. Polycrystalline CrN y with 0.93<y<1.15 and Cr 1 - x Si x N 1 . 0 2 with 0<x<0.16 were deposited by reactive magnetron sputtering. Optical reflectivity and electrical resistivity measurements indicate that the electronic properties of CrN y and Cr 1 - x Si x N 1 . 0 2 thin films are strongly dependent on their chemical composition. The main changes in the optical properties of CrN y and Cr 1 - x Si x N 1 . 0 2 films as a function of N or Si content mainly occur below 1.5 eV. Substoichiometric CrN y films with 0.93<y<0.98 exhibit room temperature resistivity ρ R T values of (1.2-7)x10 - 3 Ωcm, metallic behavior and an antiferromagnetic orthorhombic phase transition at approximately 260 K. In contrast, overstoichiometric CrN y (1.05<y<1.15) and Cr 1 - x Si x N 1 . 0 2 films exhibit ρ R T values of (1.2-4)x10 - 2 Ωcm and negative temperature coefficients of resistivity. Finally, the hardness values of CrN y films depend little on the chemical composition but are influenced by the film morphology: the nanohardness values of (111) CrN y are typically 12-14 GPa while (002) CrN y exhibit nanohardness values of 18 GPa. The addition of small amounts of Si increases the hardness values up to 22 GPa for Cr 0 . 9 4 Si 0 . 0 6 N 1 . 0 2 .