Adding Bootstrap 4 to a Rails 6 project allows you to quickly style your application with responsive layouts and ready-to-use UI components. You can integrate Bootstrap by installing it via Yarn or by including it through the asset pipeline. Once installed, you’ll need to make sure Bootstrap’s JavaScript dependencies like Popper.js and jQuery are properly configured in your Webpacker setup. After that, you can start using Bootstrap’s grid system, utilities, and prebuilt components directly in your Rails views. This setup gives your Rails app a modern, consistent design foundation while keeping customization flexible.