The security relationship and dialogue between the US and Israel is robust, mutually beneficial and unprecedented in diplomatic history in terms of its reach and depth. The trajectory of the US––Israeli security alliance continues upward, seemingly immune from the periodic political differences––even crises––that mark the overall bilateral political relationship. Hitherto, the policy implications of the security relationship appeared to flow in one direction: the US provided assistance to help Israel defend itself and project power in the region. The intensification of the bilateral security relationship was concomitant with the growth in the threat from terrorism worldwide. The US Department of Homeland Security's Office of International Affairs focused special attention on areas of cooperation with Israel. US views of Israeli nuclear policy likewise shifted during the early twenty-first century. By the end of the second decade of the twenty-first century, the US–Israeli strategic and security relationship remains firm and vibrant.