The paper is concerned with the analysis, modelling and control of a prototype self-levelling active suspension system for road vehicles. Motivation for the work is given by considering some of the fundamental performance limitations within which all traditional passive designs are constrained to operate. Self-levelling systems are presented as a viable engineering compromise from ideal ’fully active’ designs which are currently regarded as impractical owing to their associated cost and fuel-consumption penalties. Early analyses are concerned with quantifying the disturbance sources affecting automotive suspension systems : irregularities in road surface elevation and dynamic (inertial) forces resulting from driving manoeuvres such as steering and braking. Analysis of the suspension system itself includes linear and nonlinear dynamic modelling of a single wheel station or ’quarter car’, for which a suitable controller is designed. The analytical work is supported for both the active and passive suspensions by experimental results taken from a full-scale hydraulically powered quarter-car suspension test rig.