Human-computer interaction (HCI) is much broader than the study of interface design and input devices. It includes considerations of the social, political, ethical, and societal implications of computer systems. Concerns such as privacy, accessibility, universal design, and voting usability have led to active HCI research. Our examination of HCI responses to these and other issues informs a model of social engagement based on societal influences that motivate various responses from the HCI community. This model provides suggestions for engagement with issues that are likely to grow in importance over the next several years. By focusing on these issues, HCI researchers may make still greater contributions toward addressing societal concerns.