The reactive uptake kinetics of ClONO2 on pure and doped water-ice surfaces have been studied using a coated wall flow tube reactor coupled to an electron impact mass spectrometer. Experiments have been conducted on frozen film ice surfaces in the temperature range 208-228 K with P-ClONO2 <= 10(-6) Torr. The uptake coefficient (gamma) of ClONO2 on pure ice was time dependent with a maximum value of gamma(max) similar to 0.1. On HNO3-doped ice at 218 K the gamma(max) was 0.02. HOCl formation was detected in both experiments. On HCl-doped ice, uptake was gas-phase diffusion limited (gamma > 0.1) and gas-phase Cl-2 was formed. The uptake of HCl on ice continuously doped with HNO3 was reversible such that there was no net uptake of HCl once the equilibrium surface coverage was established. The data were well described by a single site 2-species competitive Langmuir adsorption isotherm. The surface coverage of HCl on HNO3-doped ice was an order of magnitude lower than on bare ice for a given temperature and P-HCl. ClONO2 uptake on this HCl/HNO3-doped ice was studied as a function Of P-HCl. gamma(max) was no longer gas-phase diffusion limited and was found to be linearly dependent on the surface concentration of HCl. Under conditions of low HCI surface concentration, hydrolysis of ClONO2 and reaction with HCI were competing such that both Cl-2 and HOCl were formed. A numerical model was used to simulate the experimental results and to aid in the parametrization of ClONO2 reactivity on cirrus ice clouds in the upper troposphere.