Klein may refer to:

• Klein (surname)
• Klein (musician)

• Klein (crater), a lunar feature
• Klein, Montana, United States
• Klein, Texas, United States
• Klein (Ohm), a river of Hesse, Germany, tributary of the Ohm
• Klein River, a river in the Western Cape province of South Africa

• Klein Bikes, a bicycle manufacturer
• Klein Tools, a manufacturer
• S. Klein, a department store
• Klein Modellbahn, an Austrian model railway manufacturer

• Klein + M.B.O., an Italian musical group
• Klein Award, for comic art
• Yves Klein, French artist

• Klein bottle, an unusual shape in topology
• Klein geometry
• Klein configuration, in geometry
• Klein cubic (disambiguation)
• Klein graphs, in graph theory
• Klein model, or Beltrami–Klein model, a model of hyperbolic geometry
• Klein polyhedron, a generalization of continued fractions to higher dimensions, in the geometry of numbers
• Klein surface, a dianalytic manifold of complex dimension 1

• Kleins, Lineman's pliers, a hand tool used by electricians and others
• Klein Technique, a movement/dance technique developed by Susan Klein and studied by Garry Stewart

• Kleine, a surname
• Kline (disambiguation)
• Cline (disambiguation)