The National Academies Forum on Traumatic Brain Injury (TBI) convened a workshop in September 2022 to explore biomarkers used to more precisely and objectively diagnose and categorize suspected TBIs. Session discussions addressed developments in TBI biomarker classes including neuroimaging, blood-based, electrophysiological, and other physiological markers; how biomarkers may be used to better guide and monitor treatment after injury; and how they can be used to refine future research studies. Speakers also discussed potential impacts of biomarkers across the trajectory of TBI care and research, efforts to translate and incorporate biomarkers from research settings into clinical practice, and opportunities to advance the field. This Proceedings of a Workshop summarizes the presentations and discussions from the event.