Check your passport. Is it due to expire soon? You may be denied entry into certain countries if your passport will expire within three to six months of your ticketed date of return. Get it renewed if you'll be cutting it close.
Contact your debit- and credit-card companies. Prior to your trip, call your bank and credit-card company to let them know which countries you'll be visiting. This will ensure that they don't decline foreign transactions. While you have them on the line, confirm your debit card's daily withdrawal limit, request an increase if you want, and ask about fees for international transactions.
Arrange your transportation. Buy tickets for any flights you might need to take within Europe as early as possible, since the cheapest seats sell out fast. Train travelers should decide whether it makes sense to buy a railpass (these cover trips in one or more countries for a set number of days); if so, you'll need to buy it before you leave the United States. If you plan to take the Eurostar between London and Paris, book tickets far ahead for the best fares.
If you're renting a car, your driver's license is all you need in most places, but some countries, including Austria, Greece, Italy and Spain, also require an International Driving Permit. While that's the letter of the law, I've rented cars in dozens of countries without an IDP -- and have never been asked to show one. You can get an IDP at your local AAA office.
Take care of medical business. Visit your doctor to get a checkup, and deal with any dental work that needs to be done. If you use prescription drugs, bring a sufficient supply to cover your trip, along with a copy of your prescription so you can refill it at a European pharmacy if necessary. Call your health insurance provider to see if they cover you internationally or whether you might need to buy special medical insurance.
Look into travel insurance. This can minimize the financial risks of a vacation. Your potential loss varies, depending on factors such as your health, how much of your trip is prepaid, the refundability of your air ticket, and what coverage you already have (through your medical, homeowners', or renters' insurance, and/or credit card).
For me, trip cancellation and interruption insurance is the most usable and worthwhile type. If I think there's a greater than 1-in-20 chance I'll need it (for instance, if I have a loved one in frail health at home), this can be a very good value and provide needed assurance. But if I'm healthy and hell-bent on making a trip, I'll risk it and not spend the extra.
Prepare gadgets for takeoff. If you plan to use your U.S. mobile phone in Europe, consider signing up for an international calling, text, and/or data plan, and confirm voice- and data-roaming fees. If you're bringing a mobile device, download any tools that might come in handy on the road, such as translators, maps, transit schedules, eBooks, Internet calling apps, and free audio tours (including mine, covering some of Europe's top sights and neighborhoods).
Make sleeping, eating, and sightseeing plans. For those who want maximum choice and peace of mind, book accommodations well before your trip, especially if you'll be traveling during peak season, major holidays, or popular festivals. To avoid long lines at major sights, such as the Eiffel Tower and Florence's Uffizi Gallery, make advance reservations online (I'll cover this topic in more depth in a future column).
The best travelers are those who plan ahead. With a little advance legwork, you'll return home with rich stories of spontaneous European adventures.
(Rick Steves (http://www.ricksteves.com) writes European travel guidebooks and hosts travel shows on public television and public radio. Email him at email@example.com and follow his blog on Facebook.)