The government and people of the United States were profoundly affected by the terrorist events of September 11, 2001. Despite the rapid succession of surveys and polls focused on people’s reactions to 9/11 that were conducted shortly after the event, much remains unknown about the details of how it affected people’s behavior and readiness for future events on a national scale. This study is based on a survey of a nationally representative sample of 3,300 households. It describes specific actions that people took to prepare for terrorism or to reduce exposure to terrorism risk during the years following 9/11, either exclusively because of the terrorism risk or for other reasons. The results show that while many individuals became more vigilant and learned more about terrorism, the threat of terrorism alone did not motivate them to take basic preparedness actions. It did, however, motivate a substantial number of people to avoid places and other things that might expose them to terrorism risk. These results elucidate the impact that 9/11 had on individual behavior and national preparedness, helping to inform future efforts to strengthen the nation’s resilience to terrorism and other extreme events.