Long-term memory (LTM) is the final stage of the dual memory model proposed by Atkinson and Shiffrin, in which data can be stored for long periods of time. While short-term and working memory persists for only about 18 to 30 seconds, information can remain in long-term memory indefinitely.

Long-term memory has also been called reference memory, because an individual must refer to the information in long-term memory when performing almost any task.

Long-term memory is commonly broken down into explicit memory (declarative), which includes episodic memory, semantic memory, and autobiographical memory, and implicit memory (procedural memory).

Long-term memory deficits occur after mild traumatic brain injury (mTBIs), and effective treatment modalities are currently unavailable.