Causation determination has become the gateway to treatment and reimbursement in workers’ compensation and personal injury cases. The science of causation is constantly evolving, which is improving our understanding of individual physical thresholds, associated risk factors, and individual biopsychosocioeconomic factors. New laws place constantly changing legal thresholds for determining work-relatedness and proximate cause. The underlying foundation for fairness is quality science to support decisions made by the legal system to provide the injured worker the appropriate treatment to restore their function and decrease their functional impairment and/or assist in determining appropriate proximate cause in personal injury cases.