Assistance in the collection of taxes enables mutual enforcement and conservancy under domestic law, subject to public policy limits. Contracting States shall mutually assist in collecting and securing tax claims: a revenue claim (tax, interest, penalties, collection costs) accepted on request must be collected or secured by the requested State under its domestic enforcement or conservancy laws as if it were its own; accepted claims gain no special priority or altered limitation treatment and their existence, validity or amount cannot be litigated in the requested State. Assistance is subject to safeguards preventing actions contrary to domestic law or public policy, requiring prior reasonable collection efforts by the requesting State, and permitting suspension or withdrawal where the claim's character changes or where assistance would be disproportionate.