Exchange of information: mandatory tax information sharing with confidentiality and explicit legal limits on disclosure. Competent authorities must exchange information necessary to implement the Convention or domestic tax laws and to prevent tax fraud or evasion; such information is to be treated as secret, used only by persons or authorities involved in tax assessment, collection, enforcement, prosecution or appeals, and may be disclosed in public court proceedings. Contracting States are not obliged to take measures contrary to their laws or practices, to provide information not obtainable under their laws or normal administration, or to disclose trade, business, industrial, commercial or professional secrets or information contrary to public policy.