Measurement of eye movements is a powerful tool for investigating perceptual and cognitive function in both infants and adults. Straightforwardly, eye movements provide a multifaceted measure of performance. For example, the location of fixations, their duration, time of occurrence, and accuracy all are potentially revealing and often allow stronger inferences than measures such as percentage correct or reaction time. Another advantage is that eye movements are an implicit measure of performance and do not necessarily involve conscious processes. Indeed, they are often a more revealing measure than conscious report (Hayhoe, Bensinger, & Ballard, 1998). Although the mere presence of gaze at a particular location in the visual field does not reveal the variety of brain computations that might be operating at that moment, the experimental context within which the fixation occurs often provides critical information that allows powerful inferences. The articles in this thematic collection are excellent examples of this. (Contains 1 figure.)