 The search for reliable indicators of biological age has been ongoing for over three decades without success until recent advances in molecular biology increased potential candidate biomarkers. This review summarizes current state-of-the-art findings on six types of biological age predictors, including epigenetic clocks, telomere length, transcriptomic and proteomic predictors, metabolomics-based predictors, and composite biomarker predictors. Promising developments consider multiple combinations of these various types of predictors, which may shed light on the aging process and provide further understanding of what contributes to healthy aging. The most promising new biological age predictor is the epigenetic clock, but its true value as a biomarker of aging requires longitudinal confirmation. This article was authored by Julia Jilhova, Nancy L. Peterson, and Sarah Hag.