Firebase CLI (Command Line Interface) is Google's official command-line tool for managing, testing, and deploying Firebase projects directly from the terminal. It provides comprehensive control over Firebase services including Hosting, Cloud Functions, Firestore, Realtime Database, Authentication, Storage, and Extensions — enabling developers to automate workflows, run local emulators, and deploy production applications. The CLI supports both interactive project initialization and non-interactive CI/CD integration, making it essential for modern Firebase development. Understanding deployment targets, emulator configuration, and service-specific commands transforms Firebase development from a console-dependent workflow into a fully scriptable, version-controlled process.