The human gaze provides paramount cues for communication and interaction. Following this insight, gaze-based interfaces have been proposed for human-computer interaction (HCI) since the early 90s, with some believing that such interfaces will revolutionize the way we interact with our devices. Since then gaze-based HCI in stationary scenarios (e. g., desktop computing) has been rapidly maturing, and the production costs of mainstream eye trackers have been steadily decreasing. In consequence, a variety of new applications with the ambitious goal to apply eye tracking to dynamic, real-world HCI tasks and scenarios have emerged. This article gives an overview of the research conducted by the Perception Engineering Group at the University of Tübingen.