Many first-generation pervasive computing systems lack the ability to evolve as new technologies emerge or as an application domain matures. Intefrating numerous heterogeneous elements is mostly a manual, ad hoc process. The environments are also closed, limiting development or extension to the original implementers. To address this limitation, the University of Florida's Mobile and Pervasive Computing Laboratory is developing programmable pervasive spaces in which a smart space exists as both a runtime environment and a software library. Service discovery and gateway protocols automatically integrate system components using generic middleware that maintains a service definition for each sensor and actuator in the space. Programmers assemble services into composite applications, which third parties can easily implement or extend. © 2005 IEEE.