To accelerate data sharing and research on traumatic brain injury (TBI), several federal agencies have been collaborating to support the development and implementation of common data elements (CDEs). The first recommendations for CDEs were made in 2010, and were well suited for hospital-based studies of acute TBI in adults. To broaden the utility of the TBI CDEs, experts were asked to update the recommendations to make them relevant to all ages, levels of injury severity, and phases of recovery. The second version of the TBI CDEs (v.2) was organized around four major study types: 1) epidemiological research; 2) studies on acute, hospitalized patients; 3) studies of the rehabilitation for moderate/severe TBI; and 4) mild TBI/concussion research. Given the heterogeneity of TBI, only a small set of core CDEs were found to be relevant across all study types. However, within groups, a much larger set of highly relevant CDEs were identified, and these were called basic CDEs. In addition, an expanded number of supplemental CDEs were specified and recommended for use depending upon the study goals. Version 2 provides a rich data dictionary for TBI research with about 900 CDEs. Many of the CDEs overlap across the study types, which will facilitate comparisons and meta-analysis across studies. Further modifications of the CDEs should be based on evaluation of their usefulness following implementation across a range of studies.