The theory of EC1, EC2, EC1E, EEC1 (or EEC1E) reactions, as well as that for a slow electron transfer is presented for a reduction in the case of polarography in the following conditions : (a) all the species are strongly adsorbed and the adsorption is fast (at equilibrium); (b) the coverage is smaller than unity, all the molecules of the oxidized form reaching the electrode are instantaneously adsorbed and all the reaction products remain attached to the electrode; (c) adsorption obeys a Langmuir isotherm. Expressions for the polarogram, the half-wave potential and the wave height (for the EC1E reaction), are derived. They can be used to diagnose the reaction type, and to calculate the electrochemical or chemical rate constants. The kinetic diagram corresponding to each case is given. The results obtained for the EEC1 (EEC1E) reaction can be extended to the case of heterogeneous electrochemical reaction with a "volume" C1 reaction.