Cognition refers to a set of mental actions or processes by which we create, use or store knowledge. We can conceptualise a global measure of overall cognitive ability, however, it is possible to distinguish a range of individual components or core cognitive domains. This is informative as cognitive disorders often selectively affect some functions, while sparing others. As well as providing diagnostic help, cognitive assessment can be valuable in monitoring progression or improvement of a disorder. It is particularly powerful used in combination with information from clinical interview and measurement of biomarkers (e.g., through brain imaging, or CSF examination).