The easiest way is to check the schedules at http://reiseauskunft… There will usually be a gray square with an “R” in a circle in it. If you click on the specific train it will say “subject to compulsory reservation” or some other wording. At the train station there’s usually an “R” on the departure board. The cheapest way is to make them at the train station. There’s usually a pictograph of a stylized seat (or a bed for overnight trains) with an “R” directing you to the appropriate window or office. It’s best to make reservations about a day in advance for day trains or about 3 days for overnight trains. Trains seldom sell out and if one does, there’s usually another train in an hour or less, so you can usually get a reservation as late as an hour before train time — but there are sometimes lines, so allow 2 hours if you’re planning to take a train that requires a reservation but haven’t bought it yet. You can buy most reservations at any major train station, so you can buy them all at once if you have a set itinerary. Another option is to avoid a trip back to the train station by buying the reservation for the train you intend to take when you leave “Paris” before you leave the station when you arrive in “Paris.” The best information I know of is at Rick Steves’ site: http://www.ricksteve… It’s a little complicated because it lists both 1st and 2nd class prices plus the inflated price to buy from a travel agent (like raileurope.com — a competitor to the folks who kindly sponsor this site) and the price to buy at the station in Europe. Most of the information is “someplace” on that site, but it’s not easy to find. The price they quote for reservations will be the inflated travel agency price and you’ll have to pay shipping and handling in addition. You can sometimes find the exact cost of a reservation by going through the “buy” option on the individual national rail company websites. There’s sometimes a “reservation only” option or a box to click indicating that you already have a ticket that will show the price.