A mnemonic device ( nih-MON-ik), or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding.

Mnemonics make use of elaborative encoding, retrieval cues, and imagery as specific tools to encode information in a way that allows for efficient storage and retrieval. Mnemonics aid original information in becoming associated with something more accessible or meaningful—which, in turn, provides better retention of the information.

Commonly encountered mnemonics are often used for lists and in auditory form, such as short poems, acronyms, initialisms, or memorable phrases, but mnemonics can also be used for other types of information and in visual or kinesthetic forms. Their use is based on the observation that the human mind more easily remembers spatial, personal, surprising, physical, sexual, humorous, or otherwise "relatable" information, rather than more abstract or impersonal forms of information.

The word "mnemonic" is derived from the Ancient Greek word μνημονικός (mnēmonikos), meaning 'of memory' or 'relating to memory' and is related to Mnemosyne ("remembrance"), the name of the goddess of memory in Greek mythology. Both of these words are derived from μνήμη (mnēmē), 'remembrance, memory'. Mnemonics in antiquity were most often considered in the context of what is today known as the art of memory.

Ancient Greeks and Romans distinguished between two types of memory: the "natural" memory and the "artificial" memory. The former is inborn, and is the one that everyone uses instinctively. The latter in contrast has to be trained and developed through the learning and practice of a variety of mnemonic techniques.

Mnemonic systems are techniques or strategies consciously used to improve memory. They help use information already stored in long-term memory to make memorization an easier task.