The Haber-Bosch process conventionally reduces N-2 to ammonia at 200 bar and 500 degrees C. Under ambient conditions, i.e., room temperature and ambient pressure, N-2 can be converted into ammonia by the nitrogenase molecule and lithium-containing solid electrodes in nonaqueous media. In this work, we explore the catalyst space for the N-2 reduction reaction under ambient conditions. We describe N-2 reduction on the basis of the *N-2 binding energy versus the *H binding energy; we find that under standard conditions, no catalyst can bind and reduce *N-2 without producing H-2. We show why a selective catalyst for N-2 reduction will also likely be selective for CO2 reduction, but N-2 reduction is intrinsically more challenging than CO2 reduction. Only by modulating the reaction pathway, like nitrogenase, or by tuning chemical potentials, like the Haber-Bosch and the Li-mediated process, N-2 can be reduced.