In this thesis, we have explained from the theoretical point of view what are progressive web applications (PWAs) and have shown in a concrete example how to transform a web application into a progressive web application. At the beginning we explained what are service workers, the most important part of PWA. They enable instant launch of PWAs, regardless of the size of the application’s content and network status. That is achieved by caching key resources. Caching allows us to eliminate network dependency and thus ensures a responsive and trustworthy user experience. We explained some of the most frequently used caching patterns. Also, we explained what is IndexedDB (local database inside the browser) and how to use it. Two new features we have highlighted are push notifications and background sync. Push notifications allow the app to continue communicating with the user even after he leaves the app. Background sync ensures that all necessary data is actually delivered to the server even in the event of temporary Internet connection loss. By writing a manifest file, we have achieved that the PWA can be installed on the user’s mobile device and placed on the home screen. Installation takes place without the user ever visiting the app store, directly from the site where that web app is running. For the purpose of demonstrating that the application works correctly regardless of whether the user has network access or not, we have introduced status identifiers that respond to network changing events and display it.