A smart environment is one that is able to identify people, interpret
their actions, and react appropriately. Thus, one of the most
important building blocks of smart environments is a person
identification system. Face recognition devices are ideal for such
systems, since they have recently become fast, cheap, unobtrusive,
and, when combined with voice-recognition, are very robust against
changes in the environment. Moreover, since humans primarily
recognize each other by their faces and voices, they feel comfortable
interacting with an environment that does the same. We present a brief
summary of the history and mathematical framework of face recognition,
the current state of the art, and present-day commercial systems. We
then describe developments towards future applications: building
interactive smart environments, augmenting human senses, skills and
memory with wearable recognition technology, and ultimately making
computers so usable, portable and intuitive that they become
ubiquitous -- the so-called ``fourth generation'' of computing.