Modern applications are constantly sending, receiving, and reacting to streams of data including internal messages, user and system events, and sensor input. Reactive Extensions (Rx) is a .NET library that abstracts away the sources of events and provides tools to effectively manage concerns like concurrency, scalability, error handling, and performance. Rx includes more than 600 operators with variants that can composed together to build reactive client and server-side applications that handle events asynchronously in a way that maximizes responsiveness, resiliency, and elasticity. Reactive Extensions in .NET is a step-by-step guide that shows developers how to build event-driven applications using the Rx library. First, it provides an overview of the design and architecture of Rx-based reactive applications. Then, it looks at the rich query capabilities that Rx provides and the Rx concurrency model that allows developers to control asynchronicity of code and processing of event handlers. The book also discusses consuming event streams, using schedulers to manage time, and working with Rx operators to filter, transform, and group events. Readers new to Rx will be able to learn from the ground up and those using Rx will get a deeper look at how to leverage Rx in existing reactive applications. Purchase of the print book includes a free eBook in PDF, Kindle, and ePub formats from Manning Publications.