Async is a utility module for Node.js and the browser that provides powerful asynchronous control flow. It offers straight-forward, battle-tested functions for common async patterns, simplifying complex asynchronous code. Async makes it easy to work with collections, control the execution order of functions, and handle errors gracefully. It provides solutions for tasks like parallel execution, serial queues, and limiting concurrency, leading to cleaner, more maintainable asynchronous JavaScript.