The US passport card works just like a regular book passport, but is handier and quicker to use in some circumstances. This card can make land and sea crossings between the US, Mexico, Canada, the Caribbean, and the Bahamas simpler. It cannot be used for overseas travel to other countries and cannot be used for many plane journeys. However, if you frequently cross the border into other countries in North America, a US passport card can be much handier. It fits easily into your wallet and can make proving your ID much simpler.
In many cases, you can apply for you US passport card by mail. This is the case if you have a US passport book already and are eligible to make use of Form DS-82. When you apply to renew your passport, you can use this form to apply for your passport card as well. Your new passport card will be sent to you by mail. If you cannot use Form DS-82 because you are not eligible or if you do not have a US passport, you must use Form DS-11 to apply for a USA passport card and you must apply in person.
If you are not sure whether you need a passport card, you may consider where you often travel and how you tend to travel. If you tend to travel by airplane, a US passport book may make more sense. If, however, you tend to travel by boat or car, and you tend to stay within the North American borders, a passport card may make things simpler.
With passport books, border security may need to check through your entire book and may need to check your book more carefully for visas and notations. With a passport card, security can get a great deal of information simply by swiping the card. Since there are no visas to check and pages to look through, the border experience is that much quicker. As well, you never have to leave your passport card behind. Since your passport card is small enough to fit in your wallet, you can bring it with you at all times. This helps prevent a common problem of leaving your passport behind. With the USA passport card, you can always have your identification with you. This means that your US passport card can also be used for other situations where proof of your citizenship or identification is required. Many people also like the fact that the passport card has relatively affordable filing fees.
If you tend to travel by plane or you tend to go overseas a lot, a passport book may make more sense. You do not have to have both the passport card and the passport book. You can simply apply for the passport book if you tend to travel more extensively.