A secret history (or shadow history) is a version of history that is at odds with commonly accepted historical events and which is claimed to have been deliberately suppressed or forgotten. Secret histories can be intended as fiction, or they can be proposed as non-fictional conspiracy theories.

The fictional genre of secret historical fiction is similar to alternate history, but with the end result of the changed historical premise being a world that is otherwise indistinguishable from the current modern day. Secret history is sometimes used in a science fiction universe to preserve continuity by reconciling predicted events in a science fiction universe with what actually happened.

The process of inventing or altering the canonical account of past events in fiction is known as retconning.

Examples of secret history in the media include:

• Blackadder — the first series has a forgotten King Richard IV of England
• Dark Skies
• The X-Files
• The Illuminatus! Trilogy by Robert Shea and Robert Anton Wilson
• The Crying of Lot 49 by Thomas Pynchon
• Declare and most other novels by Tim Powers
• Harry Paget Flashman is placed at the centre of many 19th century events by George MacDonald Fraser