A crystalline structure is a well-defined atomic structure that metals and semiconductors usually have. Crystalline structures follow a periodic pattern and they are characterized by the total symmetry of the atomic lattice.

Ions and molecules can also form crystalline structures than can be extended in three dimensions. Crystalline structures have a small unit cell that is considered as the building block for the entire structure since it is repeated continuously along the translational axes. This unit cell constitutes the well-known Bravais lattice.