The use is discussed of the quasi-steady model, based on the irrotationality of the electric field between the electroded, in electrochemical machining. The general equations are derived which describe the process. From Maxwell's equations, a non-dimensional parameter, dependent on the physical characteristics of the process, is derived. When this paramter is sufficiently small, the electric field is shown to be appromimately irrotational. A quasi-steady model is then formulated in terms of Laplace's equation togther with an equation relating the change of the mode anode surface with the electric field evaluated at the anode surface. This equation can be derived from Ohm's and Faraday's laws. Different methods for solving the associated boundary value problem are discussed.