The brain transforms information in two competing ways. Automatic processing runs independently of current goals and is based on the long-term encoding of patterns and expectations. Controlled processing is the modulation of automatic processes to reach a desired outcome, when that might not be achieved by automatic processing alone. The interplay between these processes plays an important role in determining our behaviour and internal mental states. Converging lines of evidence suggest that the control of information processing is associated with rhythmic patterns in brain activity. Following a discussion of this evidence, several experiments are presented in which brain activity during control was studied using the EEG. This high time-resolution measure of neural processing allowed event-locked wave-forms, fluctuations in the amplitude of oscillatory activity and the between-trial consistency of phase differences between signals to be measured. The book should be of use to researchers and students in cognitive neuroscience or others with an interest in the neural activity associated with cognitive control.