The spiral of silence theory is a political science and mass communication theory which states that an individual's perception of the distribution of public opinion influences that individual's willingness to express their own opinions. Also known as the theory of public opinion, the spiral of silence theory claims individuals will be more confident and outward with their opinion when they notice that their personal opinion is shared throughout a group. But if the individual notices that their opinion is unpopular with the group, they will be more inclined to be reserved and remain silent. In other words, from the individual's perspective, "not isolating themself is more important than their own judgement", meaning their perception of how others in the group perceive them is more important to themself than the need for their opinion to be heard.

According to Glynn (1995), "the major components of the spiral of silence include (1) an issue of public interest; (2) divisiveness on the issue; (3) a quasi-statistical sense that helps an individual perceive the climate of opinion as well as estimate the majority and minority opinion; (4) 'fear of isolation' from social interaction "(though, whether this is a causal factor in the willingness to speak out is contested)"; (5) an individual's belief that a minority (or 'different') opinion isolates oneself from others; and (6) a 'hardcore' group of people whose opinions are unaffected by others' opinions."

The theory is not without criticism, some arguing that its widely understood definition and parameters have not been updated to reflect the behavior of 21st century society.^[who?] Others point out that there is no room within the theory to account for variables of influence other than social isolation.

In 1974, Elisabeth Noelle-Neumann, a German political scientist, created the model called "Spiral of Silence". She believed that an "individuals willingness to express his or her opinion was a function of how he or she perceived public opinion." In 1974, Neumann and her husband founded the "Public Opinion Organization" in Germany. She was also the President of the "World Association for Public Opinion Research" from 1978 to 1980.

Noelle-Neumann evolved the spiral of silence theory from research on the 1965 West German federal election. The research, according to Noelle-Neumann, "measured a lot more than we understood." The two major parties were locked in a dead heat from December until September, with a series of questions of public perception of the election winner was showing steady, independent movement. During the final days of the election, 3 to 4% of the voters shifted in the direction of the public's perception of the winner. A similar shift happened in the 1972 election, which began the development of the spiral of silence as a theory of public opinion.

According to Shelly Neill, "Introduced in 1974, the Spiral of Silence Theory [...] explores hypotheses to determine why some groups remain silent while others are more vocal in forums of public disclosure." The spiral of silence theory suggests that "people who have believed that they hold a minority viewpoint on a public issue will remain in the background where their communication will be restrained; those who believe that they hold a majority viewpoint will be more encouraged to speak." The spiral of silence theory arose from a combination of high public uncertainty about a topic with an increase in the flow of communication.

The theory explains the formation of social norms at both the micro and macro level. "As a micro-theory, the spiral of silence examines opinion expression, controlling for people's predispositions – such as fear of isolation, and also demographic variables that have been shown to influence people's willingness to publicly express opinions on issues, such as agricultural biotechnology." This micro effect is seen in experiments such as the Asch conformity experiments, conducted as early as the 1950s, in which a group of students are asked to compare the length of lines. All but one student are coached ahead of time on what answers to give and how to behave. When the coached subjects gave unanimously incorrect answers, the dissenter tended to agree with the majority, at times even when the difference between the lines was so egregious as seven inches. On the macro level, the spiral of silence occurs if more and more members of the perceived minority fall silent. This is when public perceptions of the opinion climate begin to shift. "In other words, a person's individual reluctance to express his or her opinion, simply based on perceptions of what everyone else thinks, has important implications at the social level." As one opinion gains interest, the amount of exposure it receives increases, leading the public to believe it is the majority. The perceived minority then faces the threat and fear of isolation from society unless they conform. As the opinion gains momentum, the perceived minority falls deeper into their silence. This continues until the perceived minority no longer speaks out against it, either by presenting an image of agreement or actually conforming, and the opinion of the perceived majority ultimately becomes a social norm. Large scale effects of the spiral of silence can be seen when examining the growth of the dominant opinion within a countries political climate or other such issues.

The spiral of silence has continued to be observed and studied since then. In today's world, technology can play a key part in the spiral of silence, something that could not have been predicted at the time of its inception. For example, survey data showed that during the 2016 US presidential election, opinion congruency for democratic candidate Hillary Clinton in society at large and for republican candidate Donald Trump on Facebook had indirect associations for willingness to present one's opinion both offline and online.