The Haber–Bosch process conventionally reduces N2 to ammonia at 200 bar and 500 °C. Under ambient conditions, i.e., room temperature and ambient pressure, N2 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 N2 reduction reaction under ambient conditions. We describe N2 reduction on the basis of the *N2 binding energy versus the *H binding energy; we find that under standard conditions, no catalyst can bind and reduce *N2 without producing H2. We show why a selective catalyst for N2 reduction will also likely be selective for CO2 reduction, but N2 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, N2 can be reduced.