Brain health, as opposed to mental health, is a neglected phenomenon, less discovered but now capturing more attention. Currently, the concepts surrounding brain health are vague and no clear definition of this term exists. Assessing brain health early in life may offer insights into impending disruptions in brain function. If deteriorating or poor health of the brain is detected at a young age, therapeutic steps can be taken. The definition of brain health is "the preservation of optimal brain integrity and mental and cognitive function at a given age in the absence of overt brain diseases that affect normal brain function." Recently, cognitive age has been used as a better indicator of brain health called the "cognitive clock." This book reviews, for example, fMRI, EEG, and PET scans as well as measuring certain blood and CSF biomarker levels. A new noninvasive, cost-effective, and easily implemented tool for gauging brain health is introduced. This tool can be used in rural communities as well as in low- and middle-income countries (LMIC). This book focuses on the development of this new tool for brain health measurement as well as its cross-validation in diseased and healthy populations.