Yes. You are responsible for ensuring that you have all necessary travel documents. The required documents are based on your citizenship and country of residence.

For U.S. citizens:

Effective June 1, 2009, U.S. and Canadian Citizens are required to have a valid passport or other valid travel document to travel between the U.S. and Canada by land. For more information on requirements for travel to/from the U.S., visit http://www.travel.state.gov

Since all Hotwire Hot Rate bookings are final, we recommend confirming your passport's validity before you book.

The State Department's site can help you with getting a passport. You can also call the U.S. National Passport Information Center at (877) 4USAPPT. Please allow 6 weeks for passport application processing.

Some helpful links:

How to get a passport in less than 6 weeks
New document requirements FAQs.
For foreign country entry requirements

For non-U.S. citizens:

Your travel document requirements vary based on your citizenship and resident country. Contact the embassy or consulate of all countries you plan to visit to ensure you have everything you need. Since all Hotwire Hot Rate bookings are final, we recommend confirming the validity of all your travel documents before you book any international travel on our site.

January 1, 2008 requirements for United States entry at entry ports:

Canadian citizens: May present a valid passport issued by the Government of Canada, or a valid trusted traveler program card such as NEXUS or FAST.

Bermudan citizens: May present a passport issued by the Government of Bermuda or the United Kingdom.

Mexican citizens: Must present a passport issued by the Government of Mexico and a visa, or a valid Form DSP-150, B-1/B-2 laser visa (Border Crossing Card) **.