The equilibrium solubility of HCl in ice I-h has been measured as a function of temperature and HCl partial pressure, between -8 and -35 degrees C by doping large ice single crystals with gaseous HCl for several weeks. Results indicate that the solubility of HCI in ice is very low, much less than found in many previous studies. Its temperature and HCl partial pressure dependences are found to be X-HCl = 6.13 x 10(-10)e(2806.5/T) (P-HCl)(1/2.73) where X-HCl is the solubility in mole fraction, P-HCl is the HCl partial pressure in Pa, and T is the temperature in kelvin. The diffusion coefficient of HCl in ice is also found to be very low, about 10(-12) cm(2)/s at -15 degrees C. Extrapolations of these data yield the solidus in the temperature-composition phase diagram. The determination of the solid phase composition in equilibrium with a given gas phase composition allows the calculation of the partial enthalpy of sublimation of HCl from ice, Delta h(HCl)(s) = 63.7 +/- 7.6 kJ/mol, and of the activity of HCl in ice. Possible mechanisms of HCl incorporation in ice are discussed. Atmospheric implications concerning ozone depletion and the understanding of snow composition are examined.