Interior road noise in vehicle cabins is mainly random and broadband, and can potentially be controlled using either passive or active methods. Previous active noise control systems have typically used secondary loudspeakers that are remote from a listener's ears, however, and this has limited their useful frequency range to below about 300 Hz. An active headrest system, with closely-spaced secondary loudspeakers and error sensors, may be a practical method of increasing this frequency range, using local active sound control. This thesis presents developments of the local active control strategy, with the aim of improving the attenuation performance and the convergence stability of active headrest systems in vehicles. An active headrest system is first investigated via simulation, to understand the fundamental characteristics of local active control in enclosures. The application of a headtracking device to the active headrest system is then investigated initially to allow the active headrest system to use an appropriate plant response in order to maintain stability. The remote microphone technique is then investigated, which uses the output from fixed monitoring microphones to estimate the signals at virtual error microphones at the listener's ears, via an observation filter. It is shown that the geometry of the monitoring microphone array should be chosen considering both the spatial correlation of the primary field and the condition number of the inversion associated with the design of the observation filter. The head-tracking device and the remote microphone technique have been integrated in an active headrest system. A real-time implementation is presented of the near-field estimation and integrated active headrest system for controlling either tonal or broadband sounds. In particular, the effects of using the head-tracking device during the control have been investigated with a human listener. Measurements of the road noise and acoustic response in a large SUV have also been conducted, and these are used to predict the performance of an active headrest system under various practical conditions, with promising results.