Book excerpt: Embedded processors are the heart of embedded systems. Reconfigurable embedded processors comprise an extended instruction set that is implemented using a reconfigurable fabric (similar to a field-programmable gate array, FPGA). This book presents novel concepts, strategies, and implementations to increase the run-time adaptivity of reconfigurable embedded processors. Concepts and techniques are presented in an accessible, yet rigorous context. A complex, realistic H.264 video encoder application with a high demand for adaptivity is presented and used as an example for motivation throughout the book. A novel, run-time system is demonstrated to exploit the potential for adaptivity and particular approaches/algorithms are presented to implement it.