Biomarkers of aging refer to those biomarkers that can predict functional capacity at a later age more accurately than chronological age. Validated biomarkers of aging can enable interventions which can extend the lifespan, as any changes in the biomarkers can be observed during the life span of the organism. The levels of CD4 and CD8 memory T cells along with naive T cells are found to provide an estimate of lifespan. One of the significant biomarker of aging is the epigenetic clock, which has the capability to forecast human chronological age accurately. Some of the other prominent biomarkers of determining brain aging are proteomic clocks and neuroimaging age predictors. Furthermore, cell counts and blood chemistry can also be used for predicting chronological age accurately. This book is compiled in such a manner, that it will provide in-depth knowledge about the biomarker studies in brain aging. From theories to research to practical applications, case studies related to all contemporary topics of relevance to this area of study have been included herein. This book will provide comprehensive knowledge to the readers.