Orenstein & Koppel (normally abbreviated to "O&K") was a major German engineering company specialising in railway vehicles, escalators, and heavy equipment. It was founded on April 1, 1876, in Berlin by Benno Orenstein and Arthur Koppel.

Originally a general engineering company, O&K soon started to specialise in the manufacture of railway vehicles. The company also manufactured heavy equipment and escalators. O&K pulled out of the railway business in 1981.