Compositions and structures of sputter-deposited Cu-N films are strongly dependent on the total sputtering pressure and on the content of nitrogen gas. The Cu-N films obtained can be classified into four categories : metallic Cu-rich Cu3N films with a positive temperature coefficient of resistivity (TCR), semiconducting Cu-rich Cu3N films, semiconducting stoichiometric Cu3N films, and semiconducting N-rich Cu3N films with a negative TCR. The current-voltage curves of various Cu-N films are presented. The metallic conduction and semiconductor conduction are two main electrical conduction mechanisms for various Cu-N films. The decomposition temperature of various Cu-N films has been determined to be around 604-614 K using both thermogravimetry and dynamical measurement of electrical resistance during heating in a vacuum furnace. The great scattering of data over the electrical resistivity of Cu3N reported up to now is mainly due to the nonstoichiometry of the Cu3N. The optical band gap of stoichiometric Cu3N is determined to be around 1.8-1.9 eV, but it decreases with the decrease in the degree of stoichiometry.