Open Agent Registry, Inc. Agent Identity and Discovery (AID) is a minimal, DNS-first discovery protocol for locating agent service endpoints. Given a domain name, an AID client queries a DNS TXT record at the well-known subdomain _agent.<domain> and learns the service endpoint URI, protocol token, authentication hint, and optional metadata for that agent. This document defines the AID v1.2 record format, client discovery algorithm, exact-host lookup rules, security requirements, and IANA registrations for the `_agent` DNS node name and the `agent` service name. AID is intentionally small. After discovery, protocol- specific mechanisms such as MCP or A2A handle communication and capability negotiation.