A review of the mechanisms and characterization methods of molecular electronic transport is presented. Using self-assembled monolayers (SAMs) of alkanethiols in a nanometer-scale device structure, tunneling is unambiguously demonstrated to be the main conduction mechanism for large band gap SAMs exhibiting well-known temperature and length dependencies. Inelastic electron tunneling spectroscopy exhibits clear vibrational modes of the molecules in the device, presenting the first direct evidence of the presence of molecules in a molecular transport device and confirming the tunneling transport mechanism in alkane self-assembled monolayers.