It's the ultimate trip: circumnavigating the planet, and stopping off wherever takes your fancy. Great for travelers who want to see it all, or who are just plain indecisive. But booking a round-the-world (RTW) trip can be a complex business. Here's our guide to getting started.

How to do it

The most economical way to circumnavigate is to buy a round-the-world air ticket that uses one airline alliance. Theoretically, any routing is possible, but knowing how the RTW booking system works will make your trip cheaper. For example, the Star Alliance, a coalition of 27 airlines, offers a RTW ticket with a maximum of 15 stops. Its member airlines fly to 1185 airports in 185 countries.

There are rules: you must follow one global direction (east or west -- no backtracking); you must start and finish in the same country; and you must book all your flights before departure, though you can change them later (which may incur extra charges).

How long you need

You could whip round the world in a weekend if you flew non-stop. However, the minimum duration of most RTW tickets is ten days -- still a breathless romp. Consider stock-piling annual leave, tagging on public holidays or even arranging a sabbatical in order to take off two months, ideally six to 12. The maximum duration of a RTW ticket is one year.

When to go

The weather will never be ideal in all your stops. So, focus on what you want to do most and research conditions there: if a Himalaya trek is your highlight, don't land in Nepal mid-monsoon; if you want to swim with whale sharks off Western Australia, be there April-July. Then accept you'll be in some regions at the "wrong" time -- though this might offer unexpected benefits (for example, Zambia in wet season means lush landscapes and cheaper prices).

In general, city sightseeing can be done year-round (escape extreme heat/cold/rain in museums and cafés) but outdoor adventures are more reliant on -- and enjoyable in -- the right weather.

Where to go

The classic (and cheapest) RTW tickets flit between a few big cities, for example London -- Bangkok -- Singapore -- Sydney -- LA. If you want to link more offbeat hubs (Baku -- Kinshasa -- Paramaribo, anyone?), prices will climb considerably. The cost of the ticket is based on the total distance covered or the number of countries visited.

Remember, you don't have to fly between each point: in Australia you could land in Perth, travel overland, and fly out of Cairns. Or fly into Moscow, board the Trans-Siberian train, and fly onwards from Beijing.

Pick some personal highlights and string the rest of your itinerary around those. For instance, if you're a keen trekker, flesh out a Peru (Inca Trail), New Zealand (Milford Track) and Nepal (Everest Base Camp) itinerary with Brazil (Rio's a good access point for South America), Australia and North India.

If budget's an issue, spend more time in less expensive countries. Your daily outgoings will be far higher in Western Europe and North America than South-East Asia; Indonesia, Bolivia and India are particularly cheap.

Tips, tricks & pitfalls

-- Talk to an expert before you book: you may have an itinerary in mind but an experienced RTW flight booker will know which routings work best and cost least -- a few tweaks could mean big savings.

-- Be flexible: moving your departure date by a few days can save money; mid-week flights are generally cheaper, as are flights on Christmas Day.

-- Think about internal travel: it CAN be cheaper to book internal flights at the same time as booking your RTW ticket -- but, with the global increase of low-cost airlines, you may find it better (and more flexible) to buy them separately as you go.