This document provides an introduction to reactive programming with Reactor. It discusses some of the challenges with traditional imperative programming like blocking I/O and latency. Reactor uses asynchronous programming to improve responsiveness. It introduces key concepts like Mono and Flux for publishing 0-1 and 0-N values respectively. Examples are given for creating Mono and Flux instances. The document also mentions backpressure and how Reactor provides a high-level but valuable abstraction with readable and composable code.