AI coding agents obtain persistent context from organization, project, user, vendor, and task sources. Existing formats can carry prose, skills, or tool permissions, but they do not provide one interoperable resolution model for authority, file scope, enforceability, and audit evidence. This document defines the Agent Context Interchange Protocol (ACIP), a YAML-based format and host- resolution behavior for those sources. It defines source precedence, file matching, explicit distinctions between enforceable constraints, textual directives, and preferences, a resolution receipt, compatibility behavior for AGENTS.md and Agent Skills, and migration profiles for tools that do not natively support ACIP. ACIP does not claim that natural-language instructions can force an agent to behave; enforcement requires a host or external control at the action boundary.