---
title: "A2A (Agent2Agent protocol)"
description: "An open protocol for agents to hand tasks to one another, at version 1.0 since March 2026 and a Growth Stage project of the Linux Foundation-directed Agentic AI Foundation since August 2026."
canonical: https://aigovernanceengineer.com/glossary/a2a-agent2agent-protocol
author: "Jorge García Aibar"
license: "CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)"
doi: https://doi.org/10.5281/zenodo.22956197
version: "0.5.0"
updated: 2026-09-25
---

# A2A (Agent2Agent protocol)

An open protocol for agents to hand tasks to one another, at version 1.0 since March 2026 [1] and a Growth Stage project of the Linux Foundation-directed Agentic AI Foundation since August 2026 [2]. Servers must authenticate every request, but authorisation, and the scope and revocation of authority granted mid-task, are left to the implementer [1].

- Developed in: [ch. 23, Multi-agent systems and delegation chains](https://aigovernanceengineer.com/bok/governing-agents#multi-agent-systems-and-delegation-chains)
- Chapters: [ch. 23, AI Agents](https://aigovernanceengineer.com/bok/governing-agents)
- Contrast with: [MCP](https://aigovernanceengineer.com/glossary/mcp)
- In the glossary chapter: https://aigovernanceengineer.com/bok/glossary#t-a2a-agent2agent-protocol

## Sources

[1] Agent2Agent (A2A) Protocol Specification, v1.0 (v1.0.0 released 2026-03-12 and v1.0.1 on 2026-05-28 in github.com/a2aproject/A2A; Agent Card at /.well-known/agent-card.json, signed with JWS over JCS-canonicalised JSON; servers authenticate every request; authorisation implementation-specific; scope and revocation of in-task authorisation not defined). A2A Project (Linux Foundation). 2026-05-28. https://a2a-protocol.org/latest/specification/ (verified: primary)
[2] "A New Chapter for A2A: Joining the Agentic AI Foundation" (A2A accepted as a Growth Stage project of the Linux Foundation-directed Agentic AI Foundation, alongside MCP). A2A Project. 2026-08-27. https://a2a-protocol.org/latest/blog/2026/08/27/a-new-chapter-for-a2a-joining-the-agentic-ai-foundation/ (verified: primary)