Solid state synthesis is chemical synthesis in which the principal reactants are solids and bond formation occurs without a bulk liquid reaction phase. In organic chemistry, the reactants may be co-crystallized, ground, milled, compressed, irradiated, or heated so that molecular contact, crystal packing, defects, and diffusion govern reactivity ^[1]. Mechanochemical variants use impact or shear to create fresh interfaces and activate reactions, while topochemical reactions proceed under geometric constraints imposed by a crystal lattice ^[2]. A small amount of liquid may be added in liquid-assisted grinding, but the medium remains a solid particulate assembly rather than a homogeneous solution. The concept is distinct from solvothermal synthesis, which relies on a pressurized solvent, and from solid-phase synthesis, in which a substrate is covalently tethered to an insoluble support while reagents react from solution. Its defining features are solid reactants, interfacial or lattice-controlled transport, and reaction progress within the condensed solid state.