Stimulus is a modest JavaScript framework for enhancing server-rendered HTML with interactive behavior. Instead of building an SPA (Single Page Application) with React or Vue, Stimulus adds controllers to existing HTML: each controller listens for events (clicks, form submissions) and updates the DOM accordingly. Stimulus pairs perfectly with server-rendering frameworks (Rails, Laravel, Django) where most of the app is server-generated. It's the backbone of Hotwire, a framework combining Stimulus (interactivity) with Turbo (fast navigation) for modern web apps without the complexity of SPAs. Stimulus is ideal for teams using server-rendering frameworks. It's lightweight, easy to learn, and integrates seamlessly with Rails/Laravel/Django. The philosophy is simple: HTML is the source of truth; JavaScript enhances, not replaces. Demand for Stimulus skills is growing as more teams adopt Rails/Hotwire; it's a gateway to full-stack Rails development. Salaries are competitive ($125-180k USD senior) and growing. For Rails developers, Stimulus is increasingly table stakes.