The reactivity of ClN3 with 17 negative ions has been investigated at 300 K. The electron affinity (EA) of ClN3 was bracketed to be between that of NO2 and N-3, giving EA(ClN3) = 2.48 +/- 0.20 eV, in agreement with an electronic structure calculation. Reaction rate constants and product ion branching ratios were measured. In nearly all cases the major product of the reaction was chloride ions. Charge transfer, N-3(-) production, and 0 atom incorporation is also observed. DFT calculations of stable complexes and transition states are presented for two typical ions. Mechanistic details are discussed in terms of reaction coordinate diagrams.