Assistance in tax collection: reciprocal enforcement and conservancy under domestic law, subject to public policy and proportionality. Contracting States shall mutually assist in collecting revenue claims, defined to include taxes, interest, administrative penalties and collection costs, where taxation is not contrary to the Agreement. A requested State must accept claims for collection or conservancy at the requesting State's request and enforce them under its own laws as if they were its own claims, subject to domestic rules on enforcement, no special priority or altered time limits, exclusive jurisdiction of the requesting State's courts over validity disputes, notification if claim conditions cease, and exceptions for conflicts with law, public policy, inadequate prior measures, or disproportionate administrative burden.