A blue pencil is a pencil traditionally used by a copy editor or sub-editor to show corrections to a written copy.

Blue pencil

A red and blue copying pencil
Classification	Editing
Used with	Written copies
Inventor	[data missing]
Related	[data missing]

The colour is used specifically because it will not show in some lithographic or photographic reproduction processes, which are known as non-photo blue pencils. For similar reasons, red pencils are sometimes used since their pigment will not reproduce by xerography.

Since the introduction of electronic editing using word processors or desktop publishing, literal blue pencils are more rarely seen.