The intermolecular interactions between the amines NH3, CH3NH2, (CH3)(2)NH, and (CH3)(3)N and the ClF molecule were investigated with the aid of ab initio calculations performed at different levels of Moller-Plesset perturbation theory and coupled cluster expansions. In addition, three density functional theory approaches were probed. Medium-sized to extended polarized basis sets were applied. Distinct and very systematic differences occur for the calculated complex properties in this series when applying different electron correlation methods. In these four complexes, the computed intramolecular ClF distance is substantially widened relative to that of the isolated CIF molecule by about 0.07-0.15 Angstrom, whereas the calculated intermolecular N . . . Cl distance is substantially contracted by about 0.2-0.3 Angstrom upon going from H3N . . . ClF to (CH3)(3)N . . . ClF, in agreement with the experimentally observed trend. Computed dipole moments range from about 5.7 D in H3N . . . ClF to about 7.6 D in (CH3)(3)N . . . ClF, indicating an increasingly polar structure. Successive methyl substitution modifies the interaction energy between the amine and ClF systematically from about -9 kcal mol(-1) in H3N . . . ClF to about -20 kcal mol(-1) in the (CH3)(3)N . . . ClF complex. These complexes can be described best as charge-transfer complexes with modest intramolecular structure relaxations in the amine and with an important contribution originating from a significant stretching of the ClF molecule.