The classic way to backpack around Europe is to purchase a rail pass. This is still a budget-friendly option for most trips. However, keep in mind the following:

• Don't purchase for more days than you will use.
• Don't use the pass for short jaunts -- purchasing a single ticket may be cheaper.
• A pass allows you to get on a train, but you may not get a seat.
• For busy trains you may still need to pay a reservation fee.

The most comprehensive rail pass come from Rail Europe, or the Eurail.

You have numerous options when choosing a pass, everything from purchasing for a single country to a global pass for unlimited travel. Your best bet is to have your itinerary created ahead of time.