This chapter, as well as the next, shows you how to use Android Studio in the context of building an app called Currencies. The purpose of Currencies is to provide a convenient way to convert between foreign currencies and a user’s home currency. The typical use-case is that a user is travelling abroad and needs to either exchange money or purchase something in a foreign currency. Currency exchange rates are always fluctuating and may even change from one minute to the next, so it’s important that the user have access to the most up-to-date data. The Currencies app fetches the latest exchange rates from a web service hosted by openexchangerates.org.