This text clearly presents a multitude of variables that potentially affect the results of neuropsychological tests. THe chapter authors, all noted experts in their respective fields, begin with a general discussion of neuropsychological constructs known to impact performance on neuropsychological tests, including demographics, personality, and sociocultural factors. They then present an empirical approach to assessment. They focus on the disorders under discussion (not solely the tests that might be used in diagnosis) and reflect the contributions the field has made to detecting differences in disorders that have neurological underpinnings.The disorders reviewed include dementia, HIV-related syndromes, adult seizure disorders, toxic exposure, mild to severe brain injury, and chronic fatigue syndrome.