Magnetic materials research has entered a new and exciting period with the advent of the ternary rare-earth-iron-boron compounds, ${\mathrm{R}}_2$${\mathrm{Fe}}_{14}$B. From the fundamental physics perspective the ${\mathrm{R}}_2$${\mathrm{Fe}}_{14}$B series and its isostructural relatives comprise a rich, fascinating area for the investigation of many intrinsic properties, including magnetic structures, magnetocrystalline anisotropy, and rare-earth-transition-metal exchange interactions. Intense interest in the technological aspects of these compounds has been ignited by the fact that energy products eclipsing all previous values have been realized in practical magnets based on ${\mathrm{Nd}}_2$${\mathrm{Fe}}_{14}$B, the prototypical representative; these magnets also feature economic advantages over the earlier samarium-cobalt materials. Both facets of the ${\mathrm{R}}_2$${\mathrm{Fe}}_{14}$B systems are considered in this review.

DOI:https://doi.org/10.1103/RevModPhys.63.819