IBM's Agent Communication Protocol (ACP) provides autonomous agents with a common "wire format" for communication. It differs from MCP and A2A in its focus on agent-to-agent messaging, task hand-off, and lifecycle management. ACP is designed to be lightweight and opinionated, offering features such as dynamic discovery, task delegation, stateful sessions, security capabilities, observability, and more. The protocol is intended for use in real-world workflows, including enterprise automation, security teams, data scientists, and creative development teams. ACP can be used with various agents and frameworks, including those from IBM, Anthropic, and Google, and can be integrated into CI pipelines without changing code. The protocol's design allows for a pragmatic on-ramp to the multi-agent future, making it an attractive solution for developers working with heterogeneous agents.