  This review discusses the physics of magnetic reconnection, a process in
which the magnetic field topology changes and magnetic energy is converted to
kinetic energy, in pair plasmas in the relativistic regime. We focus on recent
progress in the field driven by theory advances and the maturity of
particle-in-cell codes. This work shows that fragmentation instabilities at the
current sheet can play a critical role in setting the reconnection speed and
affect the resulting particle acceleration, anisotropy, bulk flows, and
radiation. Then, we discuss how this novel understanding of relativistic
reconnection can be applied to high-energy astrophysical phenomena, with an
emphasis on pulsars, pulsar wind nebulae, and active galactic nucleus jets.
