The positive- and negative-ion-molecule reactions in NF3 were studied using a pulsed electron-beam mass spectrometer. It was found that the nature of bonding in the clusters F-(NF3)(n) is mainly electrostatic with the bond dissociation energies less than 8 kcal/mol. The shell formation in F-(NF3)(n) with n = 2 and 4 is suggested. It was predicted that the NF2+(NF3)(1) ion has two isomeric structures, i.e., F2N+-NF3 and F2N+-FF2N. The former was found to be more stable than the latter. These predictions were confirmed by ab initio calculations. The lower Limit of proton affinity (PA) for NF3 was determined to be 132.4 kcal/mol by measuring the temperature dependence of the rate constants for the endothermic proton-transfer reaction H+(N-2)(2) + NF3 --> NF3H+ + 2N(2). The G2+ theory gives PA = 139.6 kcal/mol.