Memory is a reconstructive process classified as explicit and implicit memory by level of awareness. Explicit memory is a conscious recollection of either episodic or semantic memory. Episodic memory is from personal experience and is context-specific while semantic memory refers to general knowledge. Implicit memory is from priming, procedure memory or skills. On-line message held by the brain is the working memory. Prospective memory is about something to be done in the future. Over-reliance on gist memory brings in false memory. The stirring of emotion has effect on encoding and consolidation. Explicit memory depends on medial temporal and prefrontal lobes. Priming impinges directly on cerebral cortex. Procedure memory or motor skills are closely related to basal ganglia. Cerebellum plays an important role in classical conditioning and complex motor learning. Age effect on memory is mainly from decreased speed and capacity of the central executive function. Age-associated memory impairment could be normal aging while mild cognitive impairment could be preclinical dementia. Alzheimer's disease starts with episodic memory, frontotemporal dementia defects semantic memory and Lewy's body dementia impairs working memory.