Lizotte v. Aviva Insurance Company of Canada, 2016 SCC 52:
Litigation privilege is a common law rule that gives rise to an immunity from disclosure for documents and communications whose dominant purpose is preparation for litigation. This privilege has sometimes been confused with solicitor‑client privilege, both at common law and in Quebec law. However, since Blank v. Canada (Minister of Justice), 2006 SCC 39,  2 S.C.R. 319, it has been settled law that solicitor‑client privilege and litigation privilege are distinct: the purpose of solicitor‑client privilege is to protect a relationship, while that of litigation privilege is to ensure the efficacy of the adversarial process; solicitor‑client privilege is permanent, whereas litigation privilege is temporary and lapses when the litigation ends; and, finally, litigation privilege applies to unrepresented parties and to non-confidential documents, and is not directed at communications between solicitors and clients as such.
Although litigation privilege is distinguishable from solicitor‑client privilege, it is nevertheless a class privilege and gives rise to a presumption of inadmissibility for a class of communications, namely those whose dominant purpose is preparation for litigation. Thus, any document that meets the conditions for the application of litigation privilege will be protected by an immunity from disclosure unless the case is one to which one of the exceptions to that privilege applies.
Litigation privilege is subject to clearly defined exceptions, not to a case‑by‑case balancing test. In the context of privileges, the exercise of balancing competing interests is associated with case‑by‑case privileges, not class privileges. The exceptions that apply to solicitor‑client privilege are all applicable to litigation privilege. These include the exceptions relating to public safety, to the innocence of the accused and to criminal communications. They also include the exception recognized in Blank for evidence of the claimant party's abuse of process or similar blameworthy conduct. Other exceptions may be identified in the future, but they will always be based on narrow classes that apply in specific circumstances.
Finally, litigation privilege can be asserted against third parties, including third party investigators who have a duty of confidentiality. It would not be appropriate to exclude third parties from the application of this privilege or to expose the privilege to the uncertainties of disciplinary and legal proceedings that could result in the disclosure of documents that would otherwise be protected. Any uncertainty in this regard could have a chilling effect on parties preparing for litigation, who may fear that documents otherwise covered by litigation privilege could be made public.