Decide what time of year you want to go on your cruise. Tourists crowd the Rhine in the summer, and villages and cities might feel too deserted in the winter. If you want to avoid the crowds but still experience the Rhine in temperate weather, go in the spring or early fall. The region's famous "Tulip Time" happens in April and early May. If you go then, you'll probably have to share the river with plenty of tourists, but you'll get to witness the spectacular colors of the region's tulips.
Choose your desired departure and arrival cities for the cruise. Most tours offer cruises that depart from and arrive at a wide variety of cities; you'll probably be able to find one that offers the itinerary you want. Airfare is often not included in cruise fares, so choose departure and arrival cities that you can fly to and from relatively cheaply and that you would enjoy exploring for a few days before or after your cruise.
Choose a tour organization and the length of your cruise. Cruising Holidays of UK (Cruisingholidays.co.uk) offers Rhine cruises that also tour parts of the Moselle and Danube rivers, traveling to Vienna, Budapest and the Black Sea.
Euro River Cruises (Eurorivercruises.com) offers tours departing from a wide variety of cities, including Paris, Bucharest, Amsterdam, Istanbul, Vienna, Basel, Prague, Zurich, Antwerp and Strasbourg. You can travel for a minimum of three nights and a maximum of 13 nights; prices range from $600 to $3,800.
Atlas River Cruise Tours (Rivercruisetours.com) offers cruises of the Rhine and Moselle rivers with lengths from eight to 24 days. Prices range from $1,200 to $8,400.