A concern for homeland defense has been with us since the inception of the Republic. However, it has changed in focus and emphasis depending on the nature of the threat we perceived. In the earliest decades the threat was from invasion by a Britain that still did not accept the results of the Revolutionary War. Later the focus shifted to concern about possible attack by ships, and during WW I and WW II, by submarines. With the advent of the intercontinental nuclear-armed bomber in 1950, our focus changed again. When we could be attacked by ballistic missiles after 1960, our concern focused on that threat. Now that we have seen that damaging attacks can be brought to the homeland 'under the radar screen', by terrorist operations, the focus has shifted again. We are now entering an era when we must address potential homeland attacks with weapons of mass destruction (WMD) that may be delivered by a range of means, depending on the source of the attack. In response to this full spectrum of attack modes, the U.S. has implemented a three-stage defense policy that integrates overseas 'offense' and homeland 'defense'. This framework for defense analysis and planning is likely to be with us into the indefinite future.