Smartphones can greatly assist travelers in several ways. Not only are they useful for calling and instead of a desktop computer while planning the trip in advance, they can also be used to check up-to-date information while you are on the go, to receive real-time updates, and to solve various problems that might come up. Some apps cost money, either in themselves or by providing for-pay services, while many are for free – although few are free software. Most apps use internet connections, watch out unless you have a high-data plan or can instruct them to only use internet by Wi-Fi.

Some of the most useful type of apps for travelers include:

• Instant messaging and VoIP apps – for keeping in touch with friends and family back home if you can't send messages or make ordinary calls, or using the apps is cheaper or more handy. The globally most used apps in this category are Facebook Messenger, WhatsApp and Telegram. Others that are important in specific countries are WeChat in China, LINE in Japan, Taiwan and Thailand, Viber in the Philippines and KakaoTalk in South Korea.
• Real-time text translator apps – for automatically translating whole segments of text from one language into another. Some of the applications in this category can use the camera to translate texts on signs and other objects, when the user points the smartphone towards them. The translation engines have improved dramatically, and now often give more or less correct translations (and more seldom gibberish), but some care is due, as they still may have gotten it all wrong. One of the most prominent apps in this category is Google Translate, which allows offline translation after downloading the desired language data.
• Real-time speech to speech translation apps – which allow two people to communicate through the application, which recognizes the spoken words and produces an audio output of the translation. Both persons will thus hear the translations. The apps generally fare worse than those translating written text, as they may misunderstand the spoken words and cannot yet use much of the additional context.

Before using these apps check your contract regarding international data roaming charges, these apps tend to transfer data continuously.

• Public transport apps – many national and regional rail and bus companies have their own useful apps that allow their customers to search for ideal routes, to find information about timetables more easily and perhaps buy tickets. There are also apps that consolidate the public transit information of several cities into one app. In some places the local transit apps only accept the local credit/debit cards for buying tickets. This is common in the US, as signified by the request for a ZIP code, and thus are not made available outside US versions of the app stores.
• Bike sharing locator apps – show where bike sharing bikes are available and where there are free slots to return the bike. Some bike sharing systems can be used only via their app, and might require access to internet, GPS and Bluetooth.
• Ride hailing apps – informal taxi services. Different ride hailing apps are popular in different countries, so look up and download the local app of choice for your trip.
• Speed trap warning apps – for warning drivers when they are about to approach speed traps or locations where traffic police might be waiting for people speeding. The apps with the latter feature usually rely on data provided by the app users. One of the most popular apps in this category is Waze. Blitzer.de works in English and German and has fixed cameras in parts of Europe and is reliable for mobile cameras in Germany, as well as giving warnings of congestions.
• Vehicle locator apps – Google Maps does this for you.
• Fuel price apps – these applications allow drivers to access current fuel prices in any desired area (given that the app has the needed data). Many of these allow users to report any price changes.

• Map apps – Smartphones nowadays come with built-in GPS navigation and map applications, which can access detailed online maps of the entire world. You can also download additional map applications which are often free; some allow you to download detailed maps, making them useful also without internet access. The map applications can help you locate the hotels, businesses and attractions. Many map applications also provide traffic reports and are able to direct you through alternative routes in case of road traffic congestion. Some applications in this category can give warnings when speeding. Some specialized mapping apps marketed to outdoor enthusiasts, most notably hunters (mainly within the US), show detailed land ownership and property lines, useful for ensuring users are on property they can legally access.

Popular apps like Google Maps, Apple Maps, and Waze usually require an internet connection, but may also offer an offline mode. Another option is using an OpenStreetMap-based app, which commonly save map data locally on the phone. OSM may also offer information not available on other maps, such as hiking trails, water fountains, or sidewalks; conversely, more popular apps may include more commercial listings and have up-to-date hours and reviews. As OSM data is user-submitted, quality may vary.

• Location Specific Apps – Locations such as museums, zoos, public transit authorities, airports, university campuses, and other large institutions may offer their own app. Features differ per app, but common functions include schedules with realtime updates on ongoing events, indoor maps, real time bus or shuttle information, and or dining information.
• Compass apps – Many smartphones nowadays are capable of working as compasses using two or three built-in sensors. This solutions is not as robust as a traditional compass, but can be handy in some situations.
• Kiwix – Allows access to all Wikivoyage articles without an Internet connection.
• For Overlanders – the iOverlander app is a community-updated app with useful destinations specific to travellers doing a road trip or having an overlanding adventure.

• Currency conversion apps – Helpful to know what is a reasonable currency conversion, to make an informed decision about what price you will accept when haggling, or to determine if the price of something. The venerable Currency app also works offline.
• Camera and photo editing apps – Almost all smartphones nowadays include a built-in camera and simple photo editing software is available. Thus you can often get away without camera and desktop computer unless you need advanced features. See Travel photography for a discussion.
• Weather forecast apps – for getting up-to-date weather information for your area, including forecasts, for a specific hour and location if you so wish. There are SMS services and web pages for the same purpose.
• Disaster alert apps – Countries exposed to natural disasters sometimes have an official app; for instance, the Japanese government offers an app that rings an alert as soon as an incoming earthquake is detected. In some countries, an SMS will be sent to all mobile phones in the affected area, regardless of the apps. There may be web pages to check regularly, with similar information.
• Camping apps - Find places to camp for the night, including free locations in many areas. These often include places to safely park your vehicle for the night if you sleep in it.
• Radio – Some phone models have an FM radio embedded. With the right app, this allows you to listen to music or news even if the cellular network goes down. These are different from the more common Internet radio apps, which rely on a constant cellular connection.
• Booking apps – Many applications allow the users to search for airline and railway tickets, hotels, car rentals, cruises, etc. The search results can usually be sorted by price (see Aggregators). Airline-, railway-, and hotel chain specific apps can be useful for specific bookings, update of flight status, special requests, etc.
• Flashlight apps – many smartphones include this as a built-in feature which turns on the phone's rear camera flash (or less often the backlight of the phone screen) on full power, making the phone useful as a flashlight when needed. Third-party apps can add features such as a strobing light for increased visibility in an emergency.
• Apps for locating particular services in an unfamiliar city, such as Wi-Fi hotspots, gyms, or restrooms.
• Rating and social badge collecting are apps for reviewing products and combined with recording your activities to collect points/badges. For example w:Untappd for beer enthusiasts.
• Banking apps – These let you monitor your balance, check for inflated fees, transfer money, and block debit/credit card use if needed. They are usually provided by the bank and can do whatever you can do with your account online. You may want to connect them to an account with limited funds, and restrict what you can do through it (you don't want to be able to take a loan at gunpoint). Using a banking app on your own phone is usually more secure than logging in from an Internet café, though if it keeps you logged in, your banking information may be vulnerable if your phone is stolen. Third-party apps will need access to your credentials and can likewise do whatever; if you get scammed via your bank's app, the bank may take some responsibility, while losing your money through a third-party app will probably be seen as gross negligence. Your app may not work from certain countries known for problems (so tell your bank about your travel plans), but a criminal may be able to get around that protection. Some apps simply act as a digital checkbook, allowing you to track expenses without accessing your account.
• Mobile payment apps or wallet apps – for paying vendors for goods or services received, usually out of a bank account, though they may sometimes be linked to a credit card instead. These are particularly popular in China, where even many stall owners in traditional street markets have adopted them. If you are planning to visit China, WeChat Pay and Alipay are the most widely used apps of this category. On relatively recent phones, Apple and Google offer a way to store your debit/credit card information and wave/tap your phone on in-store contactless payment terminals that take Visa and Mastercard to pay for purchases (subject to availability by country and card issuer).

Using the smartphone while driving, especially if you need to touch it, distracts from the traffic. For your safety, let a passenger handle it or stop for anything requiring you to think or to look away from the road. Using such devices while driving is illegal in many jurisdictions.

Many apps need, require or ask for access to location, personal data or other privileges that should not be given to programs you do not trust. Usually the problem is that the company associated with the app collects personal information, but the app could also compromise your overall security.

• Aggregators
• Computers
• Mobile phones