This document discusses solid solutions, which occur when atoms of a solute are present in the lattice of a solid solvent. It describes two types of solid solutions: substitutional and interstitial. Substitutional solid solutions can be ordered or disordered, depending on whether solute atoms randomly or regularly substitute for solvent atoms in the lattice. Interstitial solid solutions involve solute atoms fitting into the spaces between solvent atom sites in the lattice. References on inorganic structural chemistry and crystal chemistry are also provided.