In a world where there is a smartphone in every pocket, designing and building applications that can run smoothly and provide the User Experience that users will like it’s the only way to go. Reactive Programming style with RxJava will help you to beat Android Platform limitations to create astonishing Android Apps. This talk will be a practical journey from basic Reactive Programming and Observer Pattern concepts to the main feature of RxJava, with practical code examples and a real-world app. I'll show the audience how to create an Observable "from scratch", from a list or from a function we already have in our code base. Our listeners will learn how to filter an Observable sequence to create a new sequence containing only the values we want; they will learn how to apply a function to an Observable, how to concatenate, merge or zip Observables. I'll show how to enjoy RxAndroid Schedulers to overcome the threading and concurrency hell in Android. I will close the talk with a practical example about RxJava + Retrofit, to easily communicate with a REST API.