In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. Two of the vectors are perpendicular, while the third makes an angle other than 90° with the plane formed by the first two.

There exist two monoclinic Bravais lattices: the simple monoclinic and the centered monoclinic lattices.

simple monoclinic	centered monoclinic

The point groups that fall under this crystal system are listed below, followed by their representations in international notation and Schoenflies notation, and mineral examples.

name	international	Schoenflies	example
monoclinic normal		C2h	gypsum
monoclinic hemimorphic	2	C2
monoclinic hemihedral	m	C1h	sucrose