The contact behavior of various metals on n-type nitrogen-doped ultrananocrystalline diamond (UNCD) thin films has been investigated. The influences of the following parameters on the current–voltage characteristics of the contacts are presented: (1) electronegativity and work function of various metals, (2) an oxidizing acid surface cleaning step, and (3) oxide formation at the film/contact interface. Near-ideal ohmic contacts are formed in every case, while Schottky barrier contacts prove more elusive. These results counter most work discussed to date on thin diamond films, and are discussed in the context of the unique grain-boundary conductivity mechanism of the nitrogen-doped UNCD. © 2003 American Institute of Physics.