Validated tests are important assessment tools for the detection and monitoring of an individual’s level of cognitive functioning. While the psychometric properties of these tests are reliable, sensitive, and specific, the proper conduct of the assessment and interpretation of the results are crucial to the usefulness and applicability of the findings. This chapter provides an overview of some of the more widely used assessment tools. The Mini-Mental State Examination, Montreal Cognitive Assessment Scale, Elderly Cognitive Assessment Questionnaire, and Abbreviated Mental Test Score are brief screening tools effective for bedside assessments and first-level case identification in the community. The Repeatable Battery for the Assessment of Neuropsychological Status, Wechsler Adult Intelligence Scale, and Wechsler Memory Scale are longer, more detailed instruments that require a higher level of training for administration. These assessment tools, together with the clinical history, biochemical findings, and neuroimaging findings, will provide a comprehensive overview of the level of cognitive functioning and diagnostic accuracy in individuals with cognitive decline. They are also useful in investigating the efficacy of interventions, such as modulations in diet or administration of dietary components.