Memory is the ability of an organism to store, retain, and subsequently recall information. Although traditional studies of memory began in the realms of philosophy, the late nineteenth and early twentieth century put memory within the paradigms of cognitive psychology. In the recent decades, it has become one of the principal pillars of a new branch of science that represents a marriage between cognitive psychology and neuroscience, called cognitive neuroscience.
There are several ways of classifying memories, based on duration, nature and retrieval of information. From an information processing perspective there are three main stages in the formation and retrieval of memory:

• Encoding (processing and combining of received information)
• Storage (creation of a permanent record of the encoded information)
• Retrieval/Recall (calling back the stored information in response to some cue for use in some process or activity)

It is common experience that human memory may be unreliable to some degree, whether by failing to remember at all or by remembering incorrectly.

Our sense of identity, of who we are and what we have done, is tied to our memories, and it can be disturbing to have those challenged. Amnesia, Alzheimer's disease, and post-traumatic stress disorder (also known as “shell-shock”) provide examples of dramatic loss of memory, with devastating effects on the sufferer and those around them.

Memory is a complicated process, only partly understood; but research suggests that the qualities of a memory do not in and of themselves provide a reliable way to determine accuracy. For example, a vivid and detailed memory may be mistaken, and a vague memory, correct. Likewise, continuity of memory is no guarantee of truth, and disruption of memory is no guarantee of falsity. Finally, memory is believed to be a reconstructed phenomenon, and so it can often be strongly influenced by expectation (one's own or other people's), emotions, the implied beliefs of others, inappropriate interpretation, or desired outcome