The Google Agent-to-Agent (A2A) protocol is a standard for enabling multiple autonomous agents to communicate with each other securely and efficiently. A2A builds upon the Model Context Protocol (MCP), which allows models to be plugged into data sources, providing a standardized way of accessing tools. The A2A protocol enables peer-to-peer meshes as well as classic hub-and-spoke designs, allowing any compliant agent to act as a client or server. It provides features such as secure authentication, long-running task support, and modality-agnostic communication, making it suitable for various use cases including multi-agent systems, enterprise-grade controls, and less brittle orchestration. A2A is designed with the future in mind, including negotiation for video, forms, and dynamic UX, ensuring that investments survive the jump to multimodal agents. The protocol is built upon proven web standards, providing a familiar feel for backend engineers.