Abstract: Magnetic reconnection converts energy into high-speed flows, thermal and energetic particles in a broad range of systems both in the heliosphere and the broader universe. The most detailed measurements are within the heliosphere, which therefore acts as an effective laboratory for many issues related to reconnection. While the mechanisms for fast reconnection are now fairly well understood, the physics basis for the explosive onset of reconnection and the mechanisms for energy conversion are active topics. Satellite-based observations are producing important constraints on theoretical models. In solar flares the energy released is roughly equally partitioned between the thermal particles and the energetic components. In the magnetosphere and the laboratory thermal ions carry the bulk of the released energy. The MMS mission is producing unprecedented measurements in Earth's space environment that are being used to benchmark computational models. The observations of impulsive energy release in flares in the Crab Nebula precipitated a rapid increase in the interest in reconnection-driven particle acceleration in astrophysical systems. The basic physics of reconnection will be presented along with current ideas on the mechanisms for plasma heating and energetic particle production.