Acknowledging an interruption with a nod of the head is a natural and intuitive communication gesture which can be performed without significantly disturbing a primary interface activity. In this paper we describe vision-based head gesture recognition techniques and their use for common user interface commands. We explore two prototype perceptual interface components which use detected head gestures for dialog box confirmation and document browsing, respectively. Tracking is performed using stereo-based alignment, and recognition proceeds using a trained discriminative classifier. An additional context learning component is described, which exploits interface context to obtain robust performance. User studies with prototype recognition components indicate quantitative and qualitative benefits of gesture-based confirmation over conventional alternatives. Categories and Subject Descriptors I.2.10 [Artificial Intelligence]: Vision and Scene Understanding—Motion; H.5.2 [Informatio...