Summary form only given. The fundamental principles that guide pervasive computing environment design evolved with distributed systems: local area networks, middleware, wide-area networks, the WWW. Over the years, ever smaller, portable computers came on the market and wireless networking technology evolved, leading to the emergence of mobile and wireless computing. Embedded computing gave us small devices, sensors and actuators, increasingly with communications capability. There are now substantial projects that demonstrate that sensor-rich environments, such as active buildings and cities, are feasible and will be deployed widely in the real world in the near future. This issue of Pervasive Computing describes several such projects.