In contrast to more well-known constitutional isomerism, which differentiates isomers simply by the atomic connectivity, stereoisomerism generally maintains equal atomic connections and orders of building blocks as well as having the same numbers of atoms and types of elements. The difference between stereoisomers is the spatial disposition of the atoms, moving the discussion to a three-dimensional level.

Stereoisomerism contains within itself two different kinds of isomers, based on whether one stereoisomer is a mirror image of the other one or not. Molecules that satisfy the mirror-image and non-superimposable requirements are defined as enantiomers, while the others are diastereomers.