Carbonic anhydrase II (CAII) is a zinc metalloenzyme that catalyzes the hydration of CO 2 to yield bicarbonate and a proton. N-(4-Sulfamylbenzoyl)benzylamine (SBB) is a tight-binding inhibitor of human CAII with K d ) 2.1 nM. Previous X-ray crystallographic work shows that the benzyl ring of SBB makes an edge-to-face interaction with Phe-131 in the enzyme active site. We have manipulated the electrostatics of this interaction by systematically substituting electronegative fluorine atoms for the benzyl ring hydrogens of SBB. Crystal structures of 10 enzyme-inhibitor complexes have been determined to atomic resolution. Analysis of these structures reveals that the main contributions to enzyme-inhibitor affinity can be approximated by a combination of dipole-induced dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. Surprisingly, different electrostatic components dominate affinity in different enzyme-inhibitor pairs.