This chapter begins by covering issues involved with testing older adults and the neurological changes that occur during the natural aging process. It looks at some things that decline and change as people grow older. When studying memory in older adults, one issue that must be resolved is how changes in memory are to be assessed. The other way of assessing age-related changes in memory is do a longitudinal study, in which the same individuals are tested at multiple points in time. Age-related changes in neural processing have led to theories of memory and aging, known as speed theories. According to the stereotype, there are a number of age-related declines in memory. The chapter discusses changes in core memory abilities, such as changes in short-term/working memory, episodic memory, and semantic memory. It considers a number of the more prominent dementias. These include Alzheimer's disease, Parkinson's disease, Huntington's disease, and the dementia associated with multiple sclerosis.