The primary chemical equilibria which define autoprotolysis in aqueous binary solvents have been elucidated and the constants of these equilibria computed for aqueous solvent mixtures of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol, acetonitrile, acetone, tetrahydrofuran, dimethyl sulfoxide, 1,4-dioxane, and formic acid. The values of these constants explain the different behaviors of the diverse binary solvents. From these fundamental constants, the plan value at any solvent composition of any of the binary solvents studied can be accurately computed