Wiretapping, also known as wire tapping or telephone tapping, is the monitoring of telephone and Internet-based conversations by a third party, often by covert means. The wire tap received its name because, historically, the monitoring connection was an actual electrical tap on an analog telephone or telegraph line. Legal wiretapping by a government agency is also called lawful interception. Passive wiretapping monitors or records the traffic, while active wiretapping alters or otherwise affects it.

Lawful interception is officially strictly controlled in many countries to safeguard privacy; this is the case in all liberal democracies. In theory, telephone tapping often needs to be authorized by a court, and is again in theory, normally only approved when evidence shows it is not possible to detect criminal or subversive activity in less intrusive ways. Oftentimes, the law and regulations require that the crime investigated must be at least of a certain severity. Illegal or unauthorized telephone tapping is often a criminal offense. In certain jurisdictions, such as Germany and France, courts will accept illegally recorded phone calls without the other party's consent as evidence, but the unauthorized telephone tapping will still be prosecuted.

In the United States, under the Foreign Intelligence Surveillance Act, federal intelligence agencies can get approval for wiretaps from the United States Foreign Intelligence Surveillance Court, a court with secret proceedings, or in certain circumstances from the Attorney General without a court order.

The telephone call recording laws in most U.S. states require only one party to be aware of the recording, while twelve states require both parties to be aware. In Nevada, the state legislature enacted a law making it legal for a party to record a conversation if one party to the conversation consented, but the Nevada Supreme Court issued two judicial opinions changing the law and requiring all parties to consent to the recording of a private conversation for it to be legal. It is considered better practice to announce at the beginning of a call that the conversation is being recorded.

The Fourth Amendment to the United States Constitution protects privacy rights by requiring a warrant to search a person. However, telephone tapping is the subject of controversy surrounding violations of this right. There are arguments that wiretapping invades a person's personal privacy and therefore violates their Fourth Amendment rights. On the other hand, there are certain rules and regulations, which permit wiretapping. A notable example of this is the Patriot Act, which, in certain circumstances, gives the government permission to wiretap citizens. In addition, wiretapping laws vary per state, making it even more difficult to determine whether the Fourth Amendment is being violated.

In Canadian law, police are allowed to wiretap without the authorization from a court when there is the risk for imminent harm, such as kidnapping or a bomb threat. They must believe that the interception is immediately necessary to prevent an unlawful act that could cause serious harm to any person or to property. This was introduced by Rob Nicholson on February 11, 2013, and is also known as Bill C-55. The Supreme Court gave Parliament twelve months to rewrite a new law. Bill C-51 (also known as the Anti-Terrorism Act) was then released in 2015, which transformed the Canadian Security Intelligence Service from an intelligence-gathering agency to an agency actively engaged in countering national security threats.

Legal protection extends to 'private communications' where the participants would not expect unintended persons to learn the content of the communication. A single participant can legally, and covertly record a conversation. Otherwise police normally need a judicial warrant based upon probable grounds to record a conversation they are not a part of. In order to be valid wiretap authorization must state: 1) the offense being investigated by the wiretap, 2) the type of communication, 3) the identity of the people or places targeted, 4) the period of validity (60 days from issue).

In India, the lawful interception of communication by authorized law enforcement agencies (LEAs) is carried out in accordance with Section 5(2) of the Indian Telegraph Act, 1885 read with Rule 419A of Indian Telegraph (Amendment) Rules, 2007. Directions for interception of any message or class of messages under sub-section (2) of Section 5 of the Indian Telegraph Act, 1885 shall not be issued except by an order made by the Secretary to the Government of India in the Ministry of Home Affairs in the case of Government of India and by the Secretary to the State Government in-charge of the Home Department in the case of a state government. The government has set up the Centralized Monitoring System (CMS) to automate the process of lawful interception and monitoring of telecommunications technology. The government of India on 2015 December 2 in a reply to parliament question no. 595 on scope, objectives and framework of the CMS has struck a balance between national security, online privacy and free speech informed that to take care of the privacy of citizens, lawful interception and monitoring is governed by the Section 5(2) of Indian Telegraph Act, 1885 read with Rule 419A of Indian Telegraph (Amendment) Rules, 2007 wherein oversight mechanism exists in form of review committee under chairmanship of the Cabinet Secretary at Central Government level and Chief Secretary of the State at the state government level. Section 5(2) also allows the government to intercept messages that are public emergencies or for public safety.