This article seeks to determine the mechanism(s) behind the convergence of domestic counterterrorism regulations that has been noted across many Organisation for Economic Co-operation and Development (OECD) countries. Four hypotheses are developed and tested through regression analyses. These hypotheses examine (1) U.S. influence, operationalized though a unique U.S. footprint indicator; (2) national characteristics; (3) the extent to which states’ domestic structures match; and (4) international networks. We find little support that U.S. influence matters. The international influence that does exist seems to operate through networks promoting learning, especially following a rise in the general global threat level. National characteristics as a driver also find some support.