Smartphones have been to the Noughties what the internet was to the Nineties – nothing short of revolutionary. If you don't already have one, you soon will. And with a smartphone comes its innovative add-ons – apps, or applications.
Ten billion apps have been downloaded in the past three years. There are 17,000 travel apps on the market, and 160 million app-compatible devices are owned worldwide – iPhones, Androids, BlackBerrys and tablet devices such as the iPad.
There are apps that can make our holidays a little easier, others that are just a bit of fun, and many that are thoroughly pointless. The best let you do anything you can do online or with a guidebook, but more quickly and easily and while you're on the move – with maps and GPS to tell you where you are.
You can search for flights, book a hotel, see the exact location of your accommodation – you can even talk into an app and let it translate your words instantly.
Here are some of the best travel apps on the market. Prices quoted are for iPhone apps, unless otherwise stated. Many are free to download, but beware of roaming charges.
Slick, user-friendly guides to UK destinations, covering more than 30 towns and cities. The brainchild of Mark Ellingham, the founder of Rough Guides, they offer an excellent selection of expert-picked highlights in easy-to-digest nuggets, with lots of attractive photographs. There is a useful map, too.
TimeOut (£1.79 - £2.99) iPhone/iPod Touch; Android version launching later this year
The London guide is a condensed version of the magazine, with listings, reviews and useful sharing and rating tools. The rest of the guides cover everything from hotels and restaurants to tips for families, all with good map filters, "editor's picks" and by-area listings.
Condé Nast Traveller City Guides (£5.99) iPhone/iPod Touch
Bright and stylish guides split each city into districts, with colour-coded reviews and a clever to-do list tool, but the app is slightly let down by its clunky filters. Current guides include New York, Rome, Barcelona and Paris.
Lonely Planet (£3.49) Android, iPhone/iPod Touch, iPad, Nokia.
The best breadth of content, with 125 easy-to-use city guides and phrase books for iPhones and 25 "Compass Guides", augmented-reality apps for Android (£0.61), plus five e-books for the iPad.
Footprint (£3.99) iPhone/iPod Touch; Android version launching later this year.
Footprint has gone for a more exotic spread: 51 destinations, including Havana, Hanoi and La Paz, as well as more popular cities such as Cape Town and Sydney. Clear, simple listings, attractive photography, and reader reviews.
Planning and booking
This brilliant app lets users "fly" to their holiday location for a bird's-eye view of where they will be staying, or simply use it as an armchair tool to explore the world.
Berlitz Cruise Guide (£6.99) iPhone/iPod Touch and iPad
Attractive, comprehensive guide to cruise lines and ships, with Douglas Ward's straight-talking reviews, and useful sorting of vessels by size or by their suitability for different types of cruises.
Kayak (Free) Android, BlackBerry, iPad, iPhone/iPod Touch, Windows Mobile.
One of the first searching apps, and still probably the best, with clear, quick flight, hotel and car hire results, and links to allow for booking.
The Trainline (Free) Android, BlackBerry, Nokia, iPhone/iPod Touch.
Timetables and fares, with live search and bookings, plus useful "favourites" tool.
Tripit (Free) Android, iPhone/ iPod touch and BlackBerry.
A handy all-in-one app that collates all your holiday and flight confirmation emails into one travel itinerary.
Worldmate (Free; Android, BlackBerry, iPhone/iPod Touch, Windows Mobile.)
Flights and hotels search, plus collating of travel intineraries and clever click-throughs (such as to flight status and check-ins), maps and currency converter.
The Ski Club of Great Britain (Free) iPhone/iPod Touch.
Live snow reports, webcams and ski-related news.
Weather Pro (£2.49; Android, iPhone/iPod Touch and Blackberry)
Most smartphones have their own in-built weather apps, but a good add-on is this, with worldwide forecasts, satellite images and charts.
AA Hotel Guide (free; iPhone/iPod Touch)
Long list of hotels with short reviews and booking links, but an uninspiring layout and limited filter. The AA also has restaurant, b & b and pub apps.
Various tour operators have launched apps, with mixed success. Exodus (free) is one of the better ones, with a simple, stylish search for trips, plus images, descriptions, reviews and a live chat function, where you can discuss trips with Exodus staff.
On the road
Wikitude (Free) Android, iPhone/iPod touch.
One of the best " augmented reality" apps available, which lets you point your phone's camera at your surroundings and then annotates the screen with notes on local accommodation, restaurants and sites.
TomTom (£29.99-£54.99; available on iPhone/iPod touch and Windows Mobile)
The well-known satellite navigation brand is available for mobile downloads.
Google Sky Map (Free) Android, iPhone/iPod Touch.
A bit of fun when you're away; simply point your phone at the night sky and it will show the planets and constellations.
Off Exploring (Free) iPhone; iPod Touch.
This lets you quickly and easily type up a blog, add a location and photographs and post your latest on the website for friends and family to see.
National Trust (Free)
Android, iPhone/iPod Touch. A useful snapshot of trust properties to browse while you're travelling (it points out places nearby), but less helpful for planning a trip, unless you know exactly where you want to go.
Insight Guides Travel Photo (Free) iPhone/iPod Touch.
Inspiring images, updated daily, with captions and short travel tips.
Rough Guides World Lens (Free) iPad, iPhone/iPod Touch
Seemingly random but attractive selection of travel images, with descriptions and click-through to the website for more information.
Unesco World Heritage (£2.99) iPhone/iPod Touch and iPad.
A simple list, by country or classification, of Unesco heritage sites. For armchair travellers or Unesco geeks.
Xe (Free) Android, BlackBerry, iPhone/iPod Touch.
A simple, live currency converter that lets you choose your favourite currencies for comparison.
Thomas Cook What Rate (Free) Android, iPhone/iPod Touch.
An easy-to-use converter, with simplified charts and pleasant, clean design.
Earworms (£5.99) iPhone/iPod Touch.
Self-styled "revolutionary" language learning apps, these 70-minute audio lessons use mesmerising music and repetition to get your brain to remember key words and phrases. Weirdly effective.
Lonely Planet Phrasebooks (£2.39) Android, BlackBerry, iPhone/iPod Touch, Nokia, Windows Mobile.
Easy-to-use, comprehensive phrase books with more than 600 spoken and phonetically written phrases for each guide, organised into subsections.
Google translate (Free) iPhone/iPod Touch and Android.
Type or speak into your phone and let it instantly translate into 15 languages (with mixed success if you don't speak clearly).