To assist the Texas Forensic Science Commission in a pending review of traditional toolmark-comparison testimony, the Yale Law School Forensic Science Standards Practicum submitted this report on the range of approaches that courts, legal commentators, and scientists have proposed for presenting toolmark-comparison evidence in trial settings. The report addresses four major topics: (1) the case law on source attributions for firearms and other tools; (2) consensus standards from the forensic-science community; (3) expressing uncertainty when presenting source attributions; and (4) alternative modes of interpreting the microscopic similarities and differences in compared items.