Denmark had the first known radio station in the world to broadcast commercial radio from a vessel in international waters without permission from the authorities in the country that it broadcast to (Denmark in this case). The station was named Radio Mercur and began transmission on August 2nd 1958. In the Danish newspapers it was soon called a "pirate radio".

In the 1960s in the UK, the term referred to not only a perceived theft of the state-run airwaves by the unlicensed broadcasters, but also the risk-taking nature of offshore radio stations that actually operated on anchored ships or marine platforms.

A good example of this kind of activity was Radio Luxembourg located in the Grand Duchy of Luxembourg. The English language evening broadcasts from Radio Luxembourg were intentionally beamed toward the British Isles by Luxembourg licensed transmitters, while the intended audience in the United Kingdom originally listened to their radio sets by permission of a Wireless License issued by the British General Post Office (GPO). However, under terms of that Wireless License, it was an offense under the Wireless Telegraphy Act to listen to unauthorized broadcasts which possibly included those transmitted by Radio Luxembourg. Therefore as far as the British authorities were concerned, Radio Luxembourg was a "pirate radio station" and British listeners to the station were breaking the law (although as the term 'unauthorised' was never properly defined it was somewhat of a legal grey area). This did not stop British newspapers from printing programme schedules for the station, or a British weekly magazine aimed at teenage girls, "Fab 208" from promoting the deejays and their lifestyle (Radio Luxembourg's wavelength was 208 metres).

Radio Luxembourg was later joined by two other well known pirate stations received in the UK in violation of UK licensing, Radio Caroline and Radio London, both of which broadcast from vessels anchored outside of territorial limits and were therefore legitimate but unauthorised in much the same way as Luxembourg. Indeed, all three stations even had registered offices based in mainland UK.

Where actual sea faring vessels are not involved, the term pirate radio is a political term of convenience as the word "pirate" suggests an illegal venture, regardless of the broadcast's actual legal status. The radio station XERF located at Ciudad Acuña, Coahuila, Mexico, just across the Rio Grande from Del Rio, Texas, USA, is an example.

While Mexico issued radio station XERF with a license to broadcast, the power of its 250,000 watts transmitter was far greater than the maximum of 50,000 watts authorized for commercial use by the government of the United States of America. Consequently, XERF and many other radio stations in Mexico which sold their broadcasting time to sponsors of English-language commercial and religious programs, were labeled as "border blasters", but not "pirate radio stations", even though the content of many of their programs were in violation of US law. Predecessors to XERF, for instance, had originally broadcast in Kansas, advocating "goat-gland surgery" for improved masculinity, but moved to Mexico to evade US laws about advertising medical treatments, particularly unproven ones.

In 1924, New York City station WHN was accused of being an "outlaw" station by AT&T (then American Telephone and Telegraph Company) for violating trade licenses which permitted only AT&T stations to sell airtime on their transmitters. As a result of the AT&T interpretation a landmark case was heard in court, which even prompted comments from Secretary of Commerce Herbert Hoover when he took a public stand in the station's defense. Although AT&T won its case, the furor created was such that those restrictive provisions of the transmitter license were never enforced.

 Free radio

Another variation on the term pirate radio came about during the "Summer of Love" in San Francisco during the hippie days when many things were named "free". Examples include "free store", "free love" and even "free radio", which usually referred to clandestine and unlicensed land-based transmissions. These were also tagged as being pirate radio transmissions.

The term free radio crossed the Atlantic Ocean, where it was adopted by the Free Radio Association of listeners who defended the rights of the offshore "pirate radio stations" broadcasting from ships and marine structures off the coastline of the United Kingdom. However, the term free radio also has another meaning, because it differentiates between that form of licensed broadcasting supported by the sale of commercial airtime which anyone can hear free of charge, from that form of licensed commercial broadcasting (especially television) that listeners and especially viewers have to subscribe to and which is usually known as Pay TV.

Félix Guattari points out:

"Technological development, and in particular the miniaturization of transmitters and the fact that they can be put together by amateurs, 'encounters' a collective aspiration for some new means of expression."

 Félix Guattari. "Plan for the Planet". In Molecular Revolution. Psychiatry and Politics. London: Penguin Books, 1984. p. 269.

In Europe, in addition to adopting the term free radio, supportive listeners of what had been called pirate radio adopted the term offshore radio, which was usually the term used by the owners of the marine broadcasting stations.

Freebooter was yet another variation of the term pirate radio and it was sometimes used by the business press in the USA when describing marine broadcasting in Europe.

While pirate radio began as a defamatory term in Britain, it later became accepted as having a secondary meaning to describe adventurous forms of licensed broadcasting that had roots in true offshore unlicensed broadcasting. To this end the British licensing authorities have allowed both independent stations and to date even one local BBC station to use this name, while the government retained use of the term pirate radio to describe any stations on land or at sea which are broadcasting without a license and contrary to law.

Since this subject covers both national territories, international waters and international airspace, the only effective way to treat this subject is on a country by country, international waters and international airspace basis. Because the laws vary, the interpretation of the term pirate radio also varies considerably.

Questions have been raised about various types of broadcasting conducted by national governments against the interests of other national governments which have in turn created jamming stations transmitting noises on the same frequency so as to destroy the receivability of the incoming signal.

While the USA transmitted its programs towards the USSR which attempted to jam them, in 1970 the government of the United Kingdom decided to employ a jamming transmitter to drown out the incoming transmissions from the commercial station Radio North Sea International, which was based aboard the Motor Vessel (MV) Mebo II anchored off Southeast England in the North Sea.

Other examples of this type of unusual broadcasting include the Coast Guard Cutter USCGC Courier which both originated and relayed broadcasts of the Voice of America from an anchorage at the island of Rhodes, Greece to Soviet bloc countries. Balloons have been flown above Key West, Florida to support the TV transmissions of TV Martí which are directed at Cuba. Military broadcasting aircraft have been flown over Vietnam, Iraq and many other nations by the United States Air Force. The European Union financially supported a radio station broadcasting news and information into the former Yugoslavia from a ship anchored in international waters.

Pirate radio has long been synonymous with AM (LW,MW & SW) and FM (VHF) unlicensed broadcasting and "border blasting" in most parts of the world. With the advent of the internet, many conventional AM/FM radio stations have also taken to simulcasting via the web. These range from public broadcasters, licensed commercial radio, and in some countries, the 3rd tier of low power license exempt radio stations.

Despite pirate radio being known for over the air transmission, a new type of pirate radio stations now operate online. The distinguishing feature is that these online pirates will usually not pay music copyright fees, like most of their AM/FM pirate cousins. Thes online pirate radio stations will usually attract a small and loyal audience and may go unnoticed by the authorities, unlike AM/FM pirates who can easily be heard and traced on a conventional radio.

A recent case of online pirate radio was seen in the UK. Hitz Radio (UK) and not to be confused with HitzRadio.com (USA) managed to attract large amounts of mainstream media publicity in early 2007. This publicity resulted from Ryan Dunlop, the owner of the station, nominating Hitz Radio for various business awards. After this publicity, many people with radio industry knowledge began to probe the station, which had claimed "millions of fans" and tens of thousands of listeners online. These claims, along with others, were part of the portfolio put forward for the business awards. When industry insiders checked these claims, it resulted in the UK music copyright agencies PPL and MCPS-PRS Alliance chasing back fees owed by Ryan Dunlop and Hitz Radio. That in turn resulted in the audience claims to be false, based upon the amount of back dated fees owed for copyright.

Illegal use of licensed radio spectrum (also known as bootlegging in CB circles) is fairly common and takes several forms.

• Unlicensed operation -- Particularly associated with amateur radio and licensed personal communication services such as GMRS, this refers to use of radio equipment on a section of spectrum for which the equipment is designed but on which the user is not licensed to operate (most such operators are informally known as "bubble pack pirates" from the sealed plastic retail packaging common to such walkie-talkies). While piracy on the US GMRS band is, for example, widespread (some estimates have the number of total GMRS users outstripping the number of licensed users by several orders of magnitude), such use is generally only disciplined in cases where the pirate's activity interferes with a licensee. (A notable case is that of United States amateur operator and political activist Jack Gerritsen (operating under the revoked call sign KG6IRO), who was successfully prosecuted by the FCC for unlicensed operation and malicious interference )A subcategory of this is freebanding, the use of allocations nearby a legal allocation (most typically the 27MHz Citizen's Band) on modified or purpose-built gear.
• Inadvertent interference -- Common when personal communications gear is brought into countries where it is not certified to operate. Such interference results from clashing frequency allocations, and occasionally requires wholesale reallocation of an existing band due to an insurmountable interference problem; for example, the 2004 approval in Canada of the unlicensed use of the United States General Mobile Radio Service frequencies due to interference from users of FRS/GMRS radios from the United States, where Industry Canada had to transfer a number of licensed users on the GMRS frequencies to unoccupied channels to accommodate the expanded service.
• Deliberate or malicious interference -- refers to the use of two-way radio to harass or jam other users of a channel. Such behavior is widely prosecuted, especially when it interferes with mission-critical services such as aviation radio or marine VHF radio.
• Illegal equipment -- This refers to the use of illegally modified equipment or equipment not certified for a particular band. Such equipment includes illegal linear amplifiers for CB radio, antenna or circuit modifications on walkie-talkies, the use of "export" radios for freebanding, or the use of amateur radios on unlicensed bands that amateur gear is not certified for. The use of marine VHF radio gear for inland mobile radio operations is common in some countries, with enforcement difficult since marine VHF is generally the province of maritime authorities.