RxJava is a Java VM implementation of ReactiveX—a library for composing asynchronous and event-based programs by using observable sequences.

RxJava was ported from .NET to the world of Java by Netflix. After almost two years of development, a stable release of the API was made available in 2014. This stable release targets Java (Version 6 and above), Scala, JRuby, Kotlin, and Clojure.

RxJava is a single-JAR, lightweight library and focuses on Observable abstraction. It facilitates integration with a variety of external libraries, making the library align with reactive principles. Some examples are rxjava-jdbc (database calls using JDBC with RxJava Observables) and Camel RX (Camel support for Reactive Extensions using RxJava).