TL;DR: A2A protocol refers to the communications standards that allow software agents to exchange structured messages directly, without a human intermediary initiating each exchange. In advertising, A2A protocols define how a buy-side agent and a sell-side agent represent themselves, communicate deal proposals, and reach bilateral agreement. The industry framework for this is IAB Tech Lab's AAMP (Agentic Advertising Management Protocols), which builds agent communication onto existing advertising standards. A separate protocol, AdCP (Ad Context Protocol), is published by AgenticAdvertising.org.

The term "A2A" stands for agent-to-agent. It describes a class of protocol designed for machine-to-machine communication where both parties are autonomous software agents operating under human-defined instructions, rather than humans operating software manually.

A2A protocols are not new to computing. Distributed systems have used agent communication protocols for decades. What is new in advertising is the application of A2A communication to bilateral deal negotiation at the media-buying layer, where previously the communication between a buyer's system and a publisher's system was mediated by a series of intermediary platforms, each with its own proprietary interface.

What A2A protocol does in an advertising context

An advertising A2A protocol defines four things.

How agents identify themselves. A buy-side agent needs to communicate who it represents, under what mandate authority, and with what credentials. A sell-side agent needs to communicate which publisher it represents and what inventory it is authorised to offer. The protocol specifies the format for these identity claims so that agents from different systems can verify each other's credentials without a human introduction.

How proposals are structured. A deal proposal from a buy-side agent needs to carry the buyer's CPM range, inventory requirements, audience data conditions, and approval scope in a machine-readable format that the sell-side agent can evaluate against the publisher's mandate. The protocol specifies what fields a proposal must contain, in what format, so that any compliant sell-side agent can parse it.

How counterproposals and acceptances are communicated. A bilateral negotiation involves multiple exchanges: initial proposal, counterproposal, revised proposal, and final acceptance. The protocol specifies the message types for each step and the conditions under which a deal is considered agreed.

How the deal record is written. Once both parties reach agreement, the protocol specifies how the agreed terms are recorded, who holds the record, and how the record can be verified by either party after the fact.

AAMP: the advertising framework

AAMP, the Agentic Advertising Management Protocols, is IAB Tech Lab's open-source framework for agentic advertising, announced in early 2026. Rather than replacing existing standards, it adds what agents need to use them: agentic-direct for agent communication and orchestration, reference buyer and seller agents, OpenProposal for publisher products and RFP responses, and a registry example for agent discovery. Because the reference agents and specifications are open, a buy-side agent and a sell-side agent built by different companies can work from the same foundation.

According to IAB Tech Lab, AAMP's support for the Deals API covers programmatic guaranteed, preferred deals, private marketplaces and the open marketplace, as well as linear GRPs. That means agent-negotiated deals can run through the same deal types publishers already handle alongside their open auction traffic.

AdCP, the Ad Context Protocol published by AgenticAdvertising.org, is a separate protocol aimed at the same problem. It defines a set of campaign tasks that agents call over MCP or A2A. AAMP and AdCP are developing in parallel, and buyers should ask vendors which they support and at which version.

How A2A protocol differs from programmatic RTB

Real-time bidding (RTB) is also a machine-to-machine protocol, but it operates differently. In RTB, a publisher sends a bid request to many buyers simultaneously, buyers respond with a bid price within milliseconds, and the highest bid wins the impression. There is no negotiation: the buyer either bids or does not. The outcome is a price, not a bilateral agreement.

A2A negotiation for media buying is asynchronous and bilateral. The buy-side agent proposes terms to a specific sell-side agent; the sell-side agent evaluates the proposal against the publisher's parameters; either party can counter-propose; and the result, if agreement is reached, is a deal record that both parties hold. This takes longer than an RTB auction but produces a different outcome: a documented bilateral agreement rather than a transient price signal.

The two protocols address different buying scenarios. RTB addresses commodity impression buying where price discovery through auction is appropriate. A2A addresses bilateral deal negotiation where terms, not prices alone, are the subject of agreement.

What buyers need to use A2A protocol

A buyer wanting to negotiate via A2A protocol needs three things: a buy-side agent built to a shared standard such as AAMP, a mandate that the agent can operate under, and access to a marketplace or publisher sell-side agent that works to the same standard. The marketplace provides the infrastructure for the agents to communicate; the protocol ensures they can understand each other.

The mandate is the buyer's responsibility. The protocol handles the communication format. The marketplace handles the deal record infrastructure. A buyer that has those three elements in place can execute bilateral agent-to-agent deals with any publisher whose sell-side agent works to the same standard.