A proper understanding of the electrical and mechanical behavior of the system and its components is essential for the successful operation of a wind-electric pumping system. In the present article we present a formal theory of such a system, developing a framework for the determination of the steady-state operating point, as well as the study of its transient behavior, particularly at start-up. It is shown that the sufficient accumulation of kinetic energy in the wind turbine before connecting it to its load is critical for a successful start-up, even when the system has been designed to, function at optimal steady-state conditions. A detailed discussion of the start-up process in terms of stored kinetic energy in the braking power provided by both the pump and the electrical system losses is given. The results of this analysis are believed to be useful both for the steady-state design of wind-electric pumping systems, as well as the optimization of control schemes and energy capture. (C) 2003 Elsevier Ltd. All rights reserved.