Cruising has been the fastest-growing holiday choice for travellers from Britain and North America for the past decade. Annual passengers have doubled from 4.5 million in 1990 to more than nine million in 1999, and there is no sign of this growth slowing down. New cruise ships have never been built at a faster rate. Between 1995 and 2000, nearly 50 new ships were delivered and already on the order books are another 63 for the 2000- 2005 period. These 63 ships represent an investment by the cruise industry of nearly 22 billion (about £14 billion).

This is an unprecedented expansion, not just because of the number of ships but also because of their size. Most of the last 50, and the next 60-plus, will be more than 70,000-ton (a measurement of size rather than weight or displacement, by the way) and with the capacity to carry more than 2,000 passengers. A dozen will even top 100,000-ton, a size only reached for the first time in 1996 with the arrival of the 101,000-ton Carnival Destiny.

At the end of 1999, one line - Royal Caribbean - took delivery of Voyager of the Seas, the latest in a series of 1990s ships to earn the tag of the world's largest passenger ship. Only this time, she took the title by some distance. At 137,000-ton, she is three times the size Titanic was and twice the size of qe2. She also carries just short of 4,000 passengers and more than 1,000 crew - more people on a ship than at any time in cruising history - and among her huge range of entertainment facilities are an ice rink and a rock-climbing wall on the funnel. The ship immediately proved so popular that four sister vessels were ordered for delivery before 2004.

An even larger ship, provisionally named Queen Mary 2, is being built to cross the North Atlantic alongside qe2- she will also make occasional cruises. Also owned by Cunard, she will be about 150,000-ton, although she will carry fewer passengers than the Royal Caribbean ships.

Cunard itself is now owned, along with several other lines, by the US-based Carnival Corporation, which is the largest cruise company in the world. Another US-based company, Royal Caribbean International, is number two, with the UK's PO number three. Between them, they are building 36 of the 62 new ships currently on order and, overall, the number of cruise holidays on the market will increase by 50 per cent once they have all been delivered. By then, the number of worldwide cruise passengers should have increased to somewhere between 11 and 12 million.

Nearly six million of the nine million current cruise passengers come from North America, and the majority of them cruise in the Caribbean. The UK is the second largest cruise market, with nearly 750,000 passengers having taken ocean cruises in 1999. But the fastest-growing cruise market is Asia, where a local line, Star Cruises, has come from nowhere to a position where it is challenging PO for the position of third- largest cruise company. Although it has recently (early 2000) bought the US-based Norwegian Cruise Line and Orient Lines brands, Star's eponymous brand has developed exclusively in Asia. Its ships cruise out of Malaysia, Singapore, Thailand, Hong Kong, Japan and Vietnam, with some carrying Asian passengers only and others a mix of Asians, Australasians, Britons, Europeans and Americans.

Asia is also one of the destinations that features more often and more extensively in cruise line itineraries than it did a few years back. Singapore, Thailand, Hong Kong and Malaysia remain the most frequently visited countries, while first China and, more recently, Vietnam have also been opened up to cruise tourism.

Late in 1998, the South Korean shipping conglomerate Hyundai finally began operating cruises from South to North Korea. This followed tortuous political negotiations between the governments of two parts of a nation divided since the 1950s. There have been operational hiccups since then, but the cruises continue in 2000. Passengers remain exclusively South Korean, but Hyundai plans to begin selling the cruises to foreign tourists in the near future.

The huge growth in the number of cruise ships has meant that lines are constantly searching for new destinations. In the Indian Ocean, cruises are being packaged with safari holidays in East and South Africa. There are more cruises around Australia, with side tours to the Great Barrier Reef, and this trend will accelerate after the Sydney Olympics. Cruise ships were chartered in numbers to operate as hotel ships for the duration of the Games. There has been an even bigger increase in the number of ships heading for New Zealand, with its huge variety of scenic attractions, many of which are most easily accessible by sea.

The next 'in' places for cruisers will probably be South America and the Middle East. Until recently, South American cruises were limited to a few trips up the Amazon and Orinoco, voyages timed to coincide with the Rio Carnival, and, every other year or so, a long voyage right round Cape Horn. But, in the last couple of years, cruise lines have begun to offer full seasons of cruises round the Horn between Argentina and Chile and, from 2001, there will be regular weekly cruises from Santos in Brazil.

Cruises from the Middle East are still relatively rare, but this is also set to change. The authorities in Dubai have given the go ahead for a new, purpose-built cruise terminal as part of a drive to attract more ships. It is linking with other members of the United Arab Emirates and countries in the region to try and reduce red tape, particularly in the granting of group tourist visas, and to bring down the cost for ships calling at local ports. Even Iran has begun to appear on cruise itineraries, and Saudi Arabia could be next as the country gradually embraces the non- religious tourism it has eschewed in the past.

The size of many of the ships currently under construction does restrict where they can cruise. Some are even too large to transit the Panama and Suez Canals; and the number of passengers they carry is another barrier, as certain places simply do not have the infrastructure to cope with 2,000-4,000 passengers at a time.

There are, in any case, restrictions on the number of passengers allowed to land on the islands of Antarctica, so this keeps the mega-ships away. The largest to visit is Orient Lines'Marco Polo, which limits its numbers to about 500 passengers when it cruises in the region. But most of the ships that cruise there, to the Arctic and through the Northwest Passage are much smaller. They are called expedition ships, although a better term for the experience they offer is 'soft adventure' as they usually have a fair amount of home comforts on board, even if they lack the lavish entertainment facilities of the bigger ships. The most basic are the converted Soviet ice-breakers operated by Quark Expeditions, but the vessels operated by Hapag-Lloyd, Society Expeditions, Special Expeditions, Abercrombie & Kent, and Marine Expeditions offer high-quality small- ship cruise experiences. Some of the ships are of genuine five-star standard, and they all have specialist lecturers on board as well as nippy Zodiac boats to transport their passengers even closer to nature and its marine wildlife.

Slightly less adventurous but even more cerebral are the cruises of Swan Hellenic, which, after building up a reputation for high-quality cruises despite the poor quality of the ships it chartered, finally built a new ship to match its reputation. The Minerva now operates year-round around the world instead of only during summer, but the policy of hiring top lecturers in fields that include history, archaeology, botany, and architecture to accompany every cruise continues.

Ships that have their own history are also increasingly popular. Star Clippers made waves with its first two ships, both authentic recreations of turn-of-the-century clipper sailing ships. On these, passengers can help out with the rigging and even stand watches if they want to, while the captains regularly give sailing lessons.

In 2000, the same company added a third ship, the largest sailing vessel in the world and a recreation of a famous German sail ship. This will have more luxurious cabins and suites than its other ships. Some will even have butler service and their own private balconies. In fact, cabins with their own balconies is the other major trend of twenty-first-century cruising. At first only the five-star-plus cruise lines, such as Silversea, offered these but now some of the larger vessels among the less expensive ships have many cabins with this much sought-after extra.

Another important development has been the addition of alternative dining options on board the larger ships. This means there is no longer any need to eat at set times and at set tables - one of the previous downsides of cruising for some people. On this new breed of ship, there are bistros, pizzerias, grills and speciality Italian, Chinese, Japanese and Tex-Mex restaurants.

While ocean cruising grabs all the headlines, there has also been a steady growth of interest in river cruising and a major expansion in the choice of possible destinations. Although they are often spoken of in the same breath, ocean and river cruising offer quite different experiences.

Apart from their obvious appeal to those who are worried about seasickness, river cruises also offer a lot more time ashore than most ocean cruises. There are usually several stops a day, particularly on rivers such as the Rhine, which competes with the Nile to be the most popular river cruise destination of all. However, in recent years, popular new river cruise programmes have been established in many other countries, notably in Russia (the Volga - between St Petersburg and Moscow), Italy (the Po) and Portugal (the Douro).

The British and the Germans are the biggest fans of river cruising, with about 100,000 passengers apiece annually and the Danube and the Rhône among their other favourite destinations, but Americans also enjoy the experience and there have been a succession of new riverboats on the Mississippi and other US rivers. These are usually replicas of the original steamwheelers that plied these routes a century and more ago.

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