Exchange of information upon request enables cross border tax inquiries and obliges states to gather and transmit relevant taxpayer data. Article 5 requires the competent authority of the Requested Party to provide, upon request, tax relevant information and to use all relevant information gathering measures available under domestic law if existing holdings are insufficient; it may furnish depositions and authenticated originals where permitted. Authorities must be able to obtain information from banks, fiduciaries and regarding legal and beneficial ownership across entities and ownership chains, subject to limits for public companies and records beyond statutory retention. Requests must show foreseeable relevance by identifying the person, period, information sought, tax purpose, grounds for territorial or custodial control, and prior domestic efforts; the Requested Party must promptly acknowledge requests and explain delays or refusals.