Hortensius is a small, bowl-shaped lunar impact crater that is located in the northern part of the Mare Insularum.

It was named after 17th century Dutch astronomer Martin van den Hove (Latinized as Martinus Hortensius).

The interior has a higher albedo than the surrounding lunar mare, despite traces of ray material from Copernicus.

The domes are generally circular in form, with a diameter of 6–8 kilometers (4–5 mi), and rising as high as 400 meters (1300 ft).

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