Web Workers are a powerful feature of JavaScript that enable parallel execution of code in the browser, allowing for expensive computations to be performed without blocking the main thread. A fully client-side web application can leverage Web Workers with React and Redux to create a seamless user experience. The key to integrating Web Workers with React and Redux is to use a custom API, middleware, and observables to communicate between the worker thread and the main thread. This allows for efficient data exchange and population of the Redux state from the worker thread.