In broad terms, banking confidentiality is the banker's professional obligation to keep the details of a client's financial and personal affairs strictly private.
Confidentiality is a matter of both contractual agreement and public duty.
Under Swiss law, violating this professional obligation is subject to criminal prosecution. Other laws, such as those which protect privacy, safeguard confidentiality as well. Banking confidentiality is not unique to Switzerland. The idea of confidentiality in financial affairs was already incorporated into ancient law. Since the mid-nineteenth century, virtually all the governments of Western Europe have had banking confidentiality laws.