Radio jamming
The Soviets (and most of their Eastern bloc allies) used two types of jamming transmitter. Skywave jamming covered a large area but for the reasons described was of limited effectiveness. Groundwave jamming was more effective but only over a small area and was thus used only in/near major cities throughout the Eastern Bloc. Both types of jamming were less effective on higher shortwave frequencies (above 15 MHz); however, many radios sold on the domestic market in the Soviet Union didn't tune these higher bands. Skywave jamming was usually accompanied by morse signals in order to enable (coded) identification of the jamming station in order that Soviet monitoring posts could assess the effectiveness of each station.
In 1987 after decades of generally refusing to acknowledge that such jamming was even taking place the Soviets finally stopped jamming western broadcasts with the exception of RFE/RL which continued to be jammed for several months into 1988. Previously there had been periods when some individual Eastern bloc countries refrained from jamming Western broadcasts but this varied widely by time and country. In general outside of the Soviet Union itself Bulgaria was one of the most prolific operators of jamming transmitters in the Eastern bloc with East Germany and Yugoslavia the least.
While western governments may have occasionally considered jamming broadcasts from Eastern Bloc stations, it was generally accepted that doing so would be a pointless exercise. Ownership of shortwave radios was less common in western countries than in the Soviet Union where, due to the vast physical size of the country, many domestic stations were relayed on shortwave as it was the only practical way to cover remote areas. Additionally, western governments were generally less afraid of intellectual competition from the Eastern Bloc.
In Francoist Spain the dictatorship jammed for decades Radio España Independiente, the radio station of the Communist Party of Spain which broadcast from Moscow (1941–1955), Bucharest (1955–1977) and East Berlin. It was the most important clandestine broadcaster in Spain and the regime considered it a threat, since it allowed its citizens to skip the censorship of the local media. Broadcasts from East Germany to South Africa were also jammed.
In Latin America there were instances of communist radio stations such as Radio Venceremos being jammed, allegedly by the CIA, while there were short lived instances where Britain jammed some Egyptian (during the Suez Crisis), Greek (prior to Cyprus gaining independence) and Rhodesian stations. During the early years of the Northern Ireland troubles the British army regularly jammed broadcasts from both Republican and Loyalist paramilitary groups.

Post Cold War (1989–present): 

China: In 2002, China acquired  standard short-wave  radio-broadcasting equipment designed for  general public  radio-broadcasting and technical support from Thales Broadcast Multimedia, a former subsidiary of the French state-owned company Thales Group.

Thales jamming technology operates only at power levels below 500 kW (for its shortwave jamming products).
Adele Milna (BSEE) of Continental Electronics (in an audio file held at shortwave.org) claims that China has duplicated his company's 100 kW, 250 kW shortwave transmitters. It is unclear if these products were indeed duplicated or if broadcast jamming (as opposed to future product sales) were a reason for the duplication.

Iran: Debates have been raised in Iran regarding the possible health hazards of satellite jamming. Iranian officials including the health minister have claimed that jamming has no health risk for humans. However, the minister of communication has recently admitted that satellite jamming has 'serious effects' and has called for identification of jamming stations so they can put a stop to this practice. The government has generally denied any involvement in jamming and claimed they are sent from unknown sources. According to some sources, IRGC is the organization behind satellite jamming in Iran.

Russia: The Russian Armed Forces have, since the summer of 2015, begun using a multi-functional EW weapon system in Ukraine, known as Borisoglebsk 2. It is postulated that this system has defeated communications in parts of that country, including mobile telephony and GPS systems.

Other countries: Since the early 1960s, the practice of radio jamming has been very common in Cuba, blocking not only American government funded radio stations (such as Voice of America) but also Ham radio signals, and stations owned and/or operated by (or selling airtime to) Cuban exile groups transmitting from Miami, such as La Cubanisima, Radio Mambi, WWFE La Poderosa and Cadena Azul. The same practice has been applied to Radio y Televisión Martí, operated by the U.S. Information Agency since 1985.
North Korea and South Korea still regularly jam some of each other's radio (and sometimes television) stations.
Several Middle Eastern countries (particularly Iran) jam shortwave broadcasts (and even occasionally attempt to jam satellite TV signals) targeted at their countries.
Pakistan has contemplated jamming pirate radio stations operated by the Taliban in all jails across Pakistan. This decision has led to an outcry from Pakistani cellular operators, who state that most of the jails lie in urban areas with a resultant impact on the cellular service of all operators in the adjacent area of jails.
Ethiopia has jammed the DW  and VOA  transmissions as well as ESAT Ethiopian Satellite Television and Eritrean radio stations.
Vietnam jams the Vietnamese service of Radio Free Asia, Radio Đáp Lời Song Núi, some FEBC programs, mostly in Vietnamese Minority languages as well as Radio Sweden with a "siren" jammer and "bubble" jammer on FM Frequencies.
In Nigeria, the Nigerian Broadcasting Commission has claimed jamming signal of Radio Biafra.
In South Africa, the use of wireless signal jammers is illegal. There is a single exception to this rule. South Africa's State Security Cluster may, in certain instances, employ signal jammers.
In Singapore, a local Indonesian Batam Hang FM 106.0 MHz based Islamic radio station of Indonesia radio stations has jammed. Somewhat it transmits up to Singapore and Johor Bahru of Malaysia at 10 kW transmission power. Hang FM 106.0 MHz was accused by Singapore authorities for spreading extremists and terrorism propaganda, there were 4 Singaporeans detained by police under the Internal Security Act (ISA) when they attempted to move to Syria and join ISIS terrorist group. Radio Hang FM has denied this accusation. Station Manager of Hang FM Radio, Abu Yusuf, firmly rejects Hang FM Radio being linked as a media that triggers radicalism. According to him, the broadcast material is also in accordance with the understanding of Ahlussunnah wal Jamaah, which apart from rejecting radicalism, terrorism, especially ISIS, also rejects other ideas or actions that are contrary to the basic principles of the peace-loving Islamic religion. Meanwhile, Deputy Chair of the Riau Islands Regional Indonesian Broadcasting Commission (KPID), Suyono, said that while under KPID supervision, in its broadcasts Radio Hang FM actually rejected radicalism and terrorism.  Hang FM must decrease its transmission power from 10 kW to 2 kW as its service area is only in Batam. In the future, after radio frequency jamming, Singapore may ban Hang FM website, this will cause listeners cannot access Hang FM via online, even mobile app in Singapore.

In fiction: Radio jamming (or "comm jamming") is a common plot element in the Star Wars franchise. In Star Wars: Episode VI - Return of the Jedi, when the Rebel fleet approaches the Galactic Empire's force, believing themselves to be launching a surprise attack, General Lando Calrissian realizes the Empire is jamming their signals, and therefore know they are approaching.
In the film Star Trek II, after receiving a distress call from the space station Regula I, Captain Kirk attempts to establish communications, but the Enterprise's comm officer Lt. Uhura reports that further transmissions are "jammed at the source".

See also: 

References: 

External links: extensive site on radio jamming
Article on recent jammers with audio samples Archived 2011-07-21 at the Wayback Machine
Audio sample of jamming (c1982) at start of BBC World service (Russian) programme Archived 2012-02-25 at the Wayback Machine includes jamming station morse ID
Ethiopia jams VOA (2010)
Ultra Fast Folloow Jammer Description (2007) Archived 2020-08-08 at the Wayback Machine
R. Pleikys, D. Vildžiūnas. Empire of Noise (video).
Aadu Jogiaas: Disturbing soviet transmissions in August 1991.
Portable jammer is illegal. Archived 2020-02-13 at the Wayback Machine
Words: Matt Bolton, Photographs: Matt Munro The Tallinn Cables, A Glimpse Into Tallainn's Secret History of Espionage Lonely Planet Magazine, December 2011