Appium is an open-source automation framework designed for testing native, hybrid, and mobile web applications on both Android and iOS devices using a single, unified API. Built on the WebDriver protocol, it allows testers to write test scripts in multiple programming languages, making it highly adaptable to different team skill sets. Its importance in mobile testing comes from its true cross-platform capability, enabling testers to reuse the same scripts across different devices and operating systems, which significantly reduces maintenance efforts. Appium also supports real devices, emulators, and cloud-based device labs, ensuring broad test coverage. With the rapid expansion of mobile applications, Appium provides a scalable, flexible, and efficient solution for delivering high-quality mobile experiences.