High-speed electromagnetic moving-iron actuators are experimentally investigated and numerically simulated, using digitally-controlled instrumentation techniques, lumped-parameter( magnetic equivalent circuit)networks,and field (finite-element) models. Various actuator topologies, based on the moving-iron principle, that are capable of achieving very high operating speeds, are also investigated. An optically-based and digitally-controlled instrumentation technique is developed to assessth e actuatord ynamic performance.A dual voltage (microprocessor-controlled) strategy is also developed to improve actuator speed of response. A lumpedparameter model that accurately simulates, with minimum computation, the dynamic behaviour of the actuator is developed and experimentally verified. This model, whose magnetic parameters are derived from static field results, accounts for magnetic saturation, 3D effects due to width change between iron parts and transverse edge fluxes, and the dynamic coupling of the actuator system variables. A static lumped-parameterm odel is developed,i n parallel, to achieve insight into the underlying actuator design principle, and rapid predictions of the effects of parametric changes. Two-dimensional field models are developed, using a commercial finite-element package, to accurately predict the saturation levels, and to estimate the mmf/flux characteristics of each actuator component (iron and air part) and force characteristics for use in the dynamic lumped-parameter model. The 3D effects are taken into account by incorporating the results of 2D scalar potential models, in typical transverse planes, into the longitudinal (main path) solution using suitable compensation factors. Transient eddy current effects are also investigated. The study is extended by surveying various topologies of moving-iron devices, and analysing their relative performances. The objective of this investigation is to establish, quantify, and compare the factors limiting the performance, particularly the maximum accelerationr ate.