These days it's not just students on gap years who pack up their belongings in a backpack and head off around the world. Whatever your age, there is an infinite number of possible flight options and journey plans. But, with all that choice, where on earth do you start?

Excuse the silly question, but what is a round-the-world ticket?Not a silly question at all - the subject can be fearsomely complex. On the most basic level, you can't buy a ticket on a single airline that goes around the world (though United Airlines is working on it). So a round-the-world ticket is a series of flight coupons that will take you in one general direction around the globe on two or more airlines. Over the past 25 years since they were first marketed, the range of options has expanded to the point where virtually anywhere you might want to go can be "folded in" to a trip

Excuse the silly question, but what is a round-the-world ticket?Not a silly question at all - the subject can be fearsomely complex. On the most basic level, you can't buy a ticket on a single airline that goes around the world (though United Airlines is working on it). So a round-the-world ticket is a series of flight coupons that will take you in one general direction around the globe on two or more airlines. Over the past 25 years since they were first marketed, the range of options has expanded to the point where virtually anywhere you might want to go can be "folded in" to a trip

Do you mean anywhere?There are a few exceptions, notably the former Soviet Union; also, including Latin America or Africa can make the fare higher.

Outline the basic optionsThere are three main ways to assemble a round-the-world trip:

1: Using a return ticket to Australia or New Zealand that allows different stopovers in each direction. Currently, the best is the Qantas/British Airways "World Discovery" fare. Example: London - Johannesburg - Sydney - Buenos Aires - London.

2: Using a fare that allows flights on the services of specific airlines or airline alliances. The most popular example of this is the Escapade fare (using Singapore Airlines, Air New Zealand, South African Airways and Ansett Australia). A possible itinerary is London - Singapore - Bali on Singapore, Bali - Brisbane - Cairns - Sydney on Ansett and Sydney - Auckland - Honolulu - Los Angeles - London on Air New Zealand.

Other fares of this type include the Oneworld Explorer, the Star Alliance and the Navigator. These types of fare allow you a maximum mileage allowance, although some fares allow purchase of blocks of "extra miles" to add side trips.

3: A chain of tickets using which-ever airline is appropriate to fulfil any required itinerary. In its simplest form, this could be a one-way ticket on, say, Malaysia Airlines on the route London - Kuala Lumpur - Australia or New Zealand, and then a one-way ticket on Air New Zealand from there back to London, with a stop in Los Angeles.

Other examples are: London - Los Angeles (Virgin), Los Angeles - Auckland - Sydney - Hong Kong (Qantas), Hong Kong - London (Virgin). Or London - Dubai - Colombo - Singapore (SriLankan), Singapore - Bandar Seri Begawan - Brisbane (Royal Brunei), Sydney - Auckland - Fiji - Los Angeles (Air New Zealand), San Francisco - London (Virgin). This last example includes a couple of "surface sectors" from Brisbane to Sydney and Los Angeles to San Francisco. The idea of these is you make your own way between the two, either because it's fun or because you have to.

So is there a list of all the round-the-world possibilities?If such a thing exists, I haven't seen it. There are unlimited possible itineraries, often with incredibly complex pricing. Airlines and agencies have, by and large, given up printing promotional material on round-the-world fares, because fares and rules change so frequently. The best even the major agencies can muster is a few examples.

So if I'm considering a round-the-world trip, how do I start?Make a list of all the places you would like to visit, and divide these into two or three priorities, eg "musts", "would quite likes" and "could drop if these would increase price dramatically". Be aware that one or more of your chosen destinations might be better visited on a separate trip from the UK. Areas such as the Caribbean or some European cities might make the only appropriate round-the-world fare option particularly expensive.

Decide whether the order in which you visit your destinations is important - for example, if you are visiting friends or family you may have to fit in with their dates, or you may want to be in a particular city for a special event. Flights between most major destinations are usually daily, though some points are less frequently served (Rarotonga in the Cook Islands is one example).

Remember that a stopover city can also be used as a base from which to see more of the area (eg stop in Miami and drive down to the Florida Keys, or stop in Bangkok and visit Chiang Mai and Phuket).

Make brief notes as to how you're thinking of spending your time at each destination (eg for Delhi, you might want to explore the city for a couple of days, then take a three-day trip around the "Golden Triangle" to visit Agra and Jaipur, making five days altogether). Decide how long you will be away for in total but, remember, some flights may be overnight, which might affect your total by a couple of days.

Is it actually worth stopping somewhere just for one night?Unless your flights both to and from a destination are relatively short (under six hours, for example), if you are thinking of breaking your journey at all, I'd probably advise a minimum of two nights. Otherwise, you'll probably only get to see the airport and the hotel. You should also build in a day or two after a long flight to recuperate.

I've always wanted to drive between Los Angeles and San Francisco: will I have to drive (or fly) back again to continue my trip?You don't have to fly everywhere: some parts of itineraries lend themselves well to land travel. It's quite normal to fly into one place and on from another, with a "surface sector" between the two, as the airlines are remarkably relaxed about grouping cities together for fare purposes. In Australia, for example, Adelaide, Brisbane, Cairns, Melbourne and Sydney are "common-rated", which means you can fly in or out of whichever city suits you.

But your choice of airline will affect your flexibility. If you bought a ticket using Air New Zealand across the Atlantic and Pacific, as Los Angeles is its only stopover point in the USA, you would have to return to LA to fly on. However, on a Qantas/British Airways ticket, you could fly into LA on Qantas, do your drive and then pick the itinerary up again in San Francisco, which is "common-rated" with LA, and fly back to the UK from there.

And what about deciding when to go?Try to be flexible, as departing a few days (sometimes even just a day) earlier or later may result in dramatic savings. Generally, it's only your departure date from the UK which influences the fare (rather than the dates on which you take your subsequent flights). The lowest season for an itinerary visiting Australia is from April to June. But this isn't necessarily the case when chains of tickets are being used.

Can I do some flights in business class?Flying some of the longer (especially the overnight) sectors in business class might sound like a good idea. However, in practice, it will usually work out cheaper to buy a business class round-the-world ticket as there is rarely a practical way to "upgrade" specific individual sectors in a cost-effective way. But see Simon Calder's column on page 10 for a couple of ideas about how to get free upgrades.

How long can I go for?Forty hours to 365 days. Though some fares have "minimum stay" requirements, an itinerary could be arranged where you only stop for a couple of hours in each place. Most round-the-world tickets are valid for a maximum of one year from your departure date from the UK.

When I've done all that?Now you need to pass your thoughts on to a travel agent. This is like presenting a chef with some raw ingredients and seeing what they come up with. There may not be just one perfect answer for you. One possibility may be cheaper but less convenient than another. I would suggest contacting perhaps three specialist agencies, such as the ones that advertise in these pages, with the same initial information, and see how they respond to your request.

Remember that just because an agent quotes a particular fare, it doesn't mean that all the flights you want will have seats available. It is worth allowing an agent to make a "provisional" booking for you if you are happy with the fare they are offering - this is the simplest way to check availability, timings etc. But make sure that you don't have more than one agency holding reservations for you on the same flight - airlines are likely to cancel "duplicate bookings" without notice, requiring you to start again from scratch.

Do I have to start and finish in london?Not necessarily. When you're asking for a quote, I suggest that you ask for prices both from your most convenient airport and from London. Although many fares allow provincial departures at little or no extra cost, others may be significantly more expensive. Do this earlier rather than later: if the agent knows of your desire to fly from a particular UK departure point when selecting a fare for you, they might find you a better deal than if they are adding on domestic flights to a London-based itinerary. Airlines with good links from regional airports include American and Continental to the US, Emirates to Asia and Australia (a new Birmingham - Dubai flight starts in December) and KLM to just about anywhere.

And do I have to go to Australia or New Zealand?No. Routes taking in Australasia are far more commonly requested, but there are numerous possibilities across the north Pacific.

Can't I do the whole thing through the internet?By all means try, but while the internet is ideal for easy point-to-point flights, once you get into complex itineraries it quickly loses its edge. You can indeed use the internet to contact agencies by e-mail to request and receive specific quotes, but I think we're still a long way from seeing websites that can automatically quote multi-sector itineraries anywhere near as well as a properly-trained agent.

The internet can be a very useful tool for gathering information about routes particular airlines fly, possible stopover destinations (including where to stay and what to do there), ordering brochures etc, but coming up with the best round-the-world itinerary is all about good planning and interaction between the traveller(s) and a good agent.

Why do I have to go through an agent? Can't I deal directly with the airline?You can go "direct", but airline staff will often only be familiar with their own airline's routes. As no single airline flies all the way around the world, you are going to need to use more than one carrier. Also, airlines should never be able to offer fares lower than those that a specialist agency can quote. In fact, the major agencies will often be offering discounts on round-the-world fares airlines are quoting. Staff at specialist agencies spend a much higher proportion of their time organising round-the-world flights than their airline counterparts, and so (should) become much more expert as to what's what in this field.

So what help can I expect from an agent?Your agent should be able to tell you which of your "non-essential" destinations are pushing the price up. They should also be able to tell if there is anywhere else that you could include without increasing the price. They should suggest the most efficient order in which to visit the destinations to take advantage of the best value fares. They should be able to discuss the length of time you intend to stay at your stopover points with constructive (ideally first-hand) experience. Your agency should give you full details of any compulsory visas that you will need to obtain in advance, and may give you some general advice on recommended immunisations.

So they'll organise everything for me?No. You're responsible for getting health advice from your GP or a travel health specialist such as MASTA (09068 224 100). Check your passport is valid for at least six months longer than your intended departure date from any point on your itinerary. Photocopy the "information" pages of your passport and keep these copies separately. It's not a bad idea to photocopy your air tickets, as well. And don't travel without adequate insurance.

The big question: how much do they cost?You can't be expecting a simple answer. There are so many variables. You occasionally see round-the-world trips offered for less than £700 (especially for departures from mid-April to mid-June), but I would say £850 is a more realistic starting figure (rarely less than £900 for anything including Africa or South America). For Christmas departures, you'd be lucky to find much under £1,400. Business class fares start at around £2,600.

Is that with taxes included?Taxes can be broadly divided into two groups: those payable "at this end" with your ticket, and taxes payable locally when leaving your destination. When you are quoted a fare, your agent should clarify if "pre-payable" taxes have been included. If not, make sure you ask what these taxes will be. They may vary by a couple of pounds from one agent to another, but there shouldn't be a great difference. On a typical UK - Asia - Australia - US - UK itinerary, expect to pay around £70. But, in addition, you'll often have to stump up a tax at individual airports.

Can the airline put up the price once I've booked?According to the latest Office of Fair Trading ruling, once you have paid in full, the airline cannot raise the fare. Should particular fares increase, or fare rules change for the worse, airlines almost always give some notice, and all reputable agencies should contact any of their customers who have only paid deposits and offer the option of full payment so that they can issue the tickets at the original fare levels, and/or with the original rules. An example of a rule change might be where a fare that allowed four free stopovers was going to be changing to only allow two free stopovers.

What happens if I change my plans once I've booked?This depends on many things: for example, when you wish to make the change. Most travel agencies will charge fees should you wish to change what you've asked them to book. Often, these fees may be £30 or £40. Changing the route of your ticket is certainly going to attract higher charges.

However, once you are actually en route, if you contact the local office of the relevant airline, they may change dates free of charge. They may also allow you to change your route (possibly subject to a charge). Changes are, of course, subject to appropriate seat availability and must fit in with the rules of the ticket.

When should I book?In general, round-the-world fares are less liable to wild fluctuations than "normal" return fares. But "specials" are offered from time to time, usually on the simpler itineraries which offer a limited number of stops and stopover possibilities. Flights do fill up (often months in advance), and it may only need one flight to be full to scupper an entire itinerary. Apart from the very slim chance that a lower fare will be introduced, I'd definitely recommend booking as far in advance as possible.