Recent developments in stable radical chemistry have afforded "heavy atom". radicals, neutral open-shell (S = 1/2) molecular species containing heavy p-block elements (S, Se), which display solid-state magnetic properties once considered exclusive to conventional metal-based magnets. These highly spin-delocalized radicals do not associate in the solid State and yet display extensive networks of close intermolecular interactions. Spin density on the heavy atoms allows for increased isotropic and spin orbit mediated anisotropic exchange effects. Structural variations induced by Chemical modification and physical pressure, coupled with. ab-initio methods to estimate,exchange energies, have facilitated the development of predictive structure/property relationships. These results, coupled with detailed theoretical analyses and magnetic resonance spectroscopic measurements, have provided insight into the Magnetic structure of ferromagnetic and spin-canted antiferromagnetic ordered materials as well as an understanding Of the importance of spin orbit coupling contributions to Magnetic hysteresis and anisotropy. Isotropic and anisotropic ferromagnetic exchange can also be enhanced indirectly by the incorporation of heavy atoms into nonspin-bearing sites, where they can contribute to multi-orbital spin orbit coupling.