Stereochemistry is a branch of chemistry that deals with the three-dimensional arrangement of atoms in molecules and the effect of this arrangement on their chemical and physical properties. It examines the spatial orientation of atoms and groups within a molecule, as well as the relationships between different stereoisomers (molecules with the same molecular formula but different spatial arrangements). Stereochemistry is important in fields such as drug design, material science, and biochemistry, as the stereochemical properties of molecules can greatly impact their behavior and interactions with other molecules.