The mechanism of the Hantzsch ester hydrogenation of imines catalyzed by chiral BINOL-phosphoric acid has been investigated using DFT methods. Despite the importance of this reaction, there are a number of possible detailed mechanisms, and the preferred pathway has not been firmly established. Our calculations show that the catalyst not only activates the imine group for the reaction by acting as a Bronsted acid but also establishes an interaction with the Hantzsch ester that can lead to an explanation for the enantioselectivity.