Under common law, privilege is a term describing a number of rules excluding evidence that would be adverse to a fundamental principle or relationship if it were disclosed. Common law refers to law and the corresponding legal system developed through decisions of courts and similar tribunals rather than through legislative statutes or executive 
The most common form is solicitor-client privilege (attorney-client privilege under US law and client legal privilege in Australia). This article is a general survey of a Common Law legal term For a general description of the concept under US law see Attorney-client privilege. Attorney-client privilege is a legal concept that protects communications between a client and his or her Attorney and keeps those communications confidential This article is about an Australian legal term For the Commonwealth equivalent see Solicitor-client privilege; and for the United States This protects confidential communications between a client and his legal adviser for the dominant purpose of legal advice.  The rationale is that clients ought to be able to communicate freely with their lawyers, in order to facilitate the proper functioning of the legal system.
Other common forms include privilege against self-incrimination (in other proceedings), without prejudice privilege (protecting communications made in the course of negotiations to settle a legal dispute), public interest privilege (formerly Crown privilege, protecting documents necessary for the proper functioning of government), marital privilege, medical professional privilege, and priest-penitent privilege. Self-incrimination is the act of accusing oneself of a Crime for which a person can then be Prosecuted. Within legal civil procedure, prejudice refers to a loss or injury Under Common law, public-interest privilege prevents the compulsory disclosure of documents or information which is against the public interest The spousal privilege, in the United States of America comprises two separate privileges the marital confidences privilege and the spousal testimonial privilege. In the laws of many Common law jurisdictions the concept of legal Privilege, or the rule that certain conversations are so private and confidential that they cannot be used The priest penitent privilege, also known as the clergy privilege, is an application of the principle of Privileged communication that protects the contents of communications
The effect of the privilege is usually a right on the part of a party to a case, allowing them to prevent evidence from being introduced in the form of testimony from the person to whom the privilege runs. For example, a person can generally prevent his attorney from testifying about their legal relationship, even if the attorney were willing to do so. In a few instances, such as the marital privilege, the privilege is a right held by the potential witness. Thus, if a wife wishes to testify against her husband, she may do so even if he opposes this testimony; however, the wife has the privilege of refusing to testify even if the husband wishes her to do so.