This thesis investigates the heritability of scale-free, also known as fractal, brain dynamics as measured by the Hurst exponent in the rsfMRI BOLD signal in adolescents and adults, leveraging the Adolescent Brain Cognitive Development Study (ABCD Study) and Human Connectome Project (HCP). rsfMRI hurst was found to be heritable at the whole brain level and across functionally parcellated ROIs in both study populations. rsfMRI hurst heritability was found to be relatively robust in ROIs across study populations. Comparisons with heritability analyses of rsfMRI, fMRI, and sMRI data across ages and measures are considered.