Superconducting properties and electrical resistivities of NbN thin films have been studied as a function of sputtering parameters, film structure, and composition. A good correlation exists between superconductingTc's and film structure and composition regardless of the sputtering conditions used to achieve this structure. The most important parameters affectingTcare lattice parameter, crystal structure, island structure, and impurity content. Substrate temperature, Ar/N2ratio, and impurity content are the principal sputtering parameters affecting film structure, and thusTc.