The attorney-client privilege is the oldest of the privileges protecting confidential communications. It was accepted as early as during the reign of Elizabeth I. The purpose of the privilege was to prevent the attorney from being required to take an oath and testify against the client. It was then considered that such testimony against one to whom loyalty was owed would violate the attorney's honor as a gentleman.
Today, the privilege is the client's prerogative. The client, not the lawyer, holds the privilege. The client has the ultimate authority to raise or to waive the privilege. An attorney may not testify as to communications made by a client unless released by the client.
Definitions of Attorney-Client Privilege abound. Here is one of the best examples:
Attorney-client privilege protects confidential communications made both by the client and to the client.
The practical consequence of the privilege is that there can be neither compelled nor voluntary disclosure by the attorney of matters conveyed to the attorney in confidence by a client for the purpose of seeking legal advice.
Ultimately it is the client, who as the holder of the privilege, alone is entitled to decide whether to claim the privilege or waive it by disclosing privilege-protected communication.
Facts are not protected
At the same time, not everything conveyed by a client to an attorney is immune from subsequent compelled disclosure in civil litigation. Many communications that clients and attorneys alike believe will be privileged are not. Whats important to remember is that the underlying facts, regardless of their source, are not privileged and discoverable.
Only the content of communications between attorneys and their agents and clients and their agents where those communications have the purpose of seeking or giving legal advice that are privileged.
Thus foundational questions which seek to determine who was present or who authored a document or to whom it was sent are simply not encompassed within the privilege.