Propaganda is the dissemination of information aimed at influencing the opinions or behaviors of large numbers of people. As opposed to impartially providing information, propaganda in its most basic sense presents information in order to influence its audience. Propaganda often presents facts selectively (thus lying by omission) to encourage a particular synthesis, or gives loaded messages in order to produce an emotional rather than rational response to the information presented. The desired result is a change of the attitude toward the subject in the target audience to further a political agenda.

Propaganda is the deliberate, systematic attempt to shape perceptions, manipulate cognitions, and direct behavior to achieve a response that furthers the desired intent of the propagandist.

—Garth S. Jowett and Victoria O'Donnell, Propaganda and Persuasion

Propaganda is generally an appeal to emotion, contrasted to an appeal to intellect. It shares techniques with advertising and public relations. Advertising and public relations can be thought of as propaganda that promotes a commercial product or shapes the perception of an organization, person or brand, though in post-World War II usage the word "propaganda" more typically refers to political or nationalist uses of these techniques or to the promotion of a set of ideas, since the term had gained a pejorative meaning, which commercial and government entities couldn’t accept. The refusal phenomenon was eventually to be seen in politics itself by the substitution of ‘political marketing’ and other designations for ‘political propaganda’.

Poster of the 19th century Scandinavist movementPropaganda was often used to influence opinions and beliefs on religious issues, particularly during the split between the Roman Catholic Church and the Protestant churches. Propaganda has become more common in political contexts, in particular to refer to certain efforts sponsored by governments, political groups, but also often covert interests. In the early 20th century, propaganda was exemplified in the form of party slogans. Also in the early 20th century the term propaganda was also used by the founders of the nascent public relations industry to describe their activities. This usage died out around the time of World War II, as the industry started to avoid the word, given the pejorative connotation it had acquired.

The execution of British nurse Edith Cavell by the German Army in 1915 was a major theme of World War I anti-German propagandaLiterally translated from the Latin gerundive as "things which must be disseminated", in some cultures the term is neutral or even positive, while in others the term has acquired a strong negative connotation. The connotations of the term "propaganda" can also vary over time. For example, in Portuguese and some Spanish language speaking countries, particularly in the Southern Cone, the word "propaganda" usually refers to the most common manipulative media — "advertising".

In English, "propaganda" was originally a neutral term used to describe the dissemination of information in favor of any given cause. During the 20th century, however, the term acquired a thoroughly negative meaning in western countries, representing the intentional dissemination of often false, but certainly "compelling" claims to support or justify political actions or ideologies. This redefinition arose because both the Soviet Union and Germany's government under Hitler admitted explicitly to using propaganda favoring, respectively, communism and Nazism, in all forms of public expression. As these ideologies were antipathetic to liberal western societies, the negative feelings toward them came to be projected into the word "propaganda" itself.