This chapter focuses on the use of reconfigurable field-programmable gate arrays (FPGAs), the advantages of using their reconfiguration capabilities concurrently with normal operation, the different reconfiguration alternatives, and the existing commercial and industrial approaches. The configuration possibilities offered by FPGAs created a new paradigm in digital circuit design, since the same device can be adapted to provide different functions by just reconfiguring it. Although reconfigurable systems are not limited to just FPGA-based ones, these are the most significant at commercial level. The first FPGA devices could only be (re)configured by downloading into them a full bitstream, which would overwrite all configuration bits in the device. Partial reconfiguration is a valuable feature for systems operating in environments where applications cannot be interrupted while the system is being reconfigured. A special subset within run-time reconfigurable systems (RTRSs) is composed of systems that can reconfigure themselves, which are referred to as self-reconfigurable systems (SRSs).