Reiner is a lunar impact crater on the Oceanus Procellarum, in the western part of the Moon.

Outside the rim is a hummocky rampart that extends out across the mare for about half a crater diameter.

To the west-northwest of the crater on the Oceanus Procellarum is the unusual feature Reiner Gamma, a fish-shaped surface marking of ray-like material with a high albedo.

[1] It is named after the astronomer Vincentio Reinieri, a disciple of Galileo Galilei.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Reiner.