The computer user of today operates in situations very unlike those of the computer user from the 1980s, when PCs sat atop desks in staid office environments that provided ample lighting, comfortable seating, controlled temperatures, and minimal noise or distraction. Computer users of today, by contrast, are likely to be using a touch screen device, perhaps while on-the-go, perhaps outside, perhaps surrounded by attention-grabbers like people, traffic lights, curbs, and signs. Users might be trying to interact while carrying luggage, wearing gloves, squinting in bright sunlight, or wiping rainwater from their screens. Unfortunately, however, today's mobile devices know little about these challenging situations, and offer even less to users by way of help or support for interaction. A useful perspective is to view these challenges through the lens of ability, disability, and accessibility, given that these notions involve the interplay of personal, environmental, contextual, and social factors. In this view, people can be "situationally impaired," as their abilities and resources for action are diminished by context. In this talk, I present the conceptual and historical foundations for situationally-induced impairments and disabilities, including the rightly controversial aspects of this notion. I distinguish situation, context, and environment, and define a space of impairments that broadens accessibility to include everyone, not just people with disabilities. Having established the foundations for this work, I then tour a handful of my projects in which mobile devices are given enhanced situation- and user-awareness (without adding custom sensors), resulting in new capabilities and improved interactions. By the end, I hope to have convincingly motivated the need for our mobile devices to become much more situationally-aware, better supporting users as a result.