This is a guide on Reactive programming. It begins by explaining to the reader what Reactive programming is and where it is used. Callbacks usually propagate themselves, leading to a callback hell. The reader is guided on how to handle callback hell. Futures and promises, which are very essential in Reactive programming are discussed in detail, thus, you will learn how to use them when programming. Implicit and explicit declarations are also explored in detail. Streams are an important aspect of Reactive programming. This guides explores stream processing in detail, thus, you will learn how to do it. You will learn how to use Vert.x for Reactive programming. The Actor model is also explained. You will learn how to organize the actors into a hierarchy and deal with relations between the parents and the children. The reactive extensions for various programming languages such as C++ and JavaScript are explored, and you will learn how to use them. A sample app is created, meaning that you will learn to use Reactive programming to create apps which can be used in real life. The following topics are discussed: - A Brief Overview of Reactive Programming - Callback Hell - Futures and Promises - Implicit and Explicit Declarations - Stream Processing - Using Vert.x for Reactive Programming - The Actor Model - Reactive Extensions - A Sample App