Electron transport through molecular junctions (a molecule coordinated to two electrodes) is a non-equilibrium phenomenon, and corresponds to a current/voltage spectroscopy. We discuss such transport in two different limits. In the scanning tunneling microscope limit, where the coupling to one electrode is very much stronger than that to the other, the density of states (DOS) along the molecule effectively dominates the transport. However, when the couplings to the two electrodes are comparable, then the DOS itself is inadequate to determine either mechanism or magnitude of transport. The DOS still describes the quantum interference effects and the statistical aspects of transport, but the actual mechanism is described by another factor, that we call the transmittance. This transmittance function modulates the DOS, due to the effects of electronic structure changes (and, though not explored here, other couplings through interelectronic correlations or vibronic coupling). In the limit of transport outside of the band, the superexchange-type exponential decay with length enters not through the DOS, but through the transmittance function.