An opinion poll, often simply referred to as a survey or a poll, is a human research survey of public opinion from a particular sample. Opinion polls are usually designed to represent the opinions of a population by conducting a series of questions and then extrapolating generalities in ratio or within confidence intervals. A person who conducts polls is referred to as a pollster.

The first known example of an opinion poll was a tally of voter preferences reported by the Raleigh Star and North Carolina State Gazette and the Wilmington American Watchman and Delaware Advertiser prior to the 1824 presidential election, showing Andrew Jackson leading John Quincy Adams by 335 votes to 169 in the contest for the United States presidency. Since Jackson won the popular vote in that state and the national popular vote, such straw votes gradually became more popular, but they remained local, usually citywide phenomena.

In 1916, The Literary Digest embarked on a national survey (partly as a circulation-raising exercise) and correctly predicted Woodrow Wilson's election as president. Mailing out millions of postcards and simply counting the returns, The Literary Digest also correctly predicted the victories of Warren Harding in 1920, Calvin Coolidge in 1924, Herbert Hoover in 1928, and Franklin Roosevelt in 1932.

Then, in 1936, its survey of 2.3 million voters suggested that Alf Landon would win the presidential election, but Roosevelt was instead re-elected by a landslide. George Gallup's research found that the error was mainly caused by participation bias; those who favored Landon were more enthusiastic about returning their postcards. Furthermore, the postcards were sent to a target audience who were more affluent than the American population as a whole, and therefore more likely to have Republican sympathies. At the same time, Gallup, Archibald Crossley and Elmo Roper conducted surveys that were far smaller but more scientifically based, and all three managed to correctly predict the result. The Literary Digest soon went out of business, while polling started to take off. Roper went on to correctly predict the two subsequent reelections of President Franklin D. Roosevelt. Louis Harris had been in the field of public opinion since 1947 when he joined the Elmo Roper firm, then later became partner.

In September 1938, Jean Stoetzel, after having met Gallup, created IFOP, the Institut Français d'Opinion Publique, as the first European survey institute in Paris. Stoetzel started political polls in summer 1939 with the question "Why die for Danzig?", looking for popular support or dissent with this question asked by appeasement politician and future collaborationist Marcel Déat.

Gallup launched a subsidiary in the United Kingdom that was almost alone in correctly predicting Labour's victory in the 1945 general election: virtually all other commentators had expected a victory for the Conservative Party, led by wartime leader Winston Churchill. The Allied occupation powers helped to create survey institutes in all of the Western occupation zones of Germany in 1947 and 1948 to better steer denazification. By the 1950s, various types of polling had spread to most democracies.

Viewed from a long-term perspective, advertising had come under heavy pressure in the early 1930s. The Great Depression forced businesses to drastically cut back on their advertising spending. Layoffs and reductions were common at all agencies. The New Deal furthermore aggressively promoted consumerism, and minimized the value of (or need for) advertising. Historian Jackson Lears argues that "By the late 1930s, though, corporate advertisers had begun a successful counterattack against their critics." They rehabilitated the concept of consumer sovereignty by inventing scientific public opinion polls, and making it the centerpiece of their own market research, as well as the key to understanding politics. George Gallup, the vice president of Young and Rubicam, and numerous other advertising experts, led the way. Moving into the 1940s, the industry played a leading role in the ideological mobilization of the American people in fighting the Nazis and the Japanese in World War II. As part of that effort, they redefined the "American Way of Life" in terms of a commitment to free enterprise. "Advertisers", Lears concludes, "played a crucial hegemonic role in creating the consumer culture that dominated post-World War II American society."

If we ask a yes-no question of a sample of people selected randomly from a large population, then the proportion of the sample that respond "yes" will be close to the true proportion, ${\displaystyle p}$, of the whole population who would have said "yes" had all of them been asked.