Since the inception of the computing paradigm, the prevalent metaphor for a computer has been that of a multi-purpose tool, as exemplified by the use of “command lines” and “desktops” at the interface between humans and computers. The unparalleled prevalence of computing-enabled devices in our everyday lives, and the widespread access to information over the Web, suggests a more apt metaphor for a modern computer, that of an assistant. Humans no longer use, but rather collaborate with their devices to solve a cognitive task, with each party learning and adapting to the capabilities of the other. Communication and decision-making happens at a level that is transparent to, and cognitively-compatible with, human abilities and limitations. One no longer speaks of human-computer interaction, but of human-computer symbiosis.