Products and processes of ionization in water vapor have been studied with the apparatus previously used by Smyth and Stueckelberg for other gases. Results of previous investigators have been confirmed and extended. Two I. P.'s for H2O+ are reported, 12.7, and 16.0 volts. Other positive ions in much smaller numbers appear as follows: H+ at 18.9, OH+ at 18.9, H3O+ with H2O+, O+ at 18.5, H+2 at 33.5, and O+2 (very weak). The probable processes of ionization involved are discussed. Negative ions observed include OH-, O-, and H-. Lozier's observation of a critical electron speed for the formation of H- is confirmed and discussed.