In American politics and advertising, the term astroturfing describes formal public relations projects which deliberately seek to engineer the impression of spontaneous, grassroots behavior. The goal is the appearance of independent public reaction to a politician, political group, product, service, event, or similar entities by centrally orchestrating the behavior of many diverse and geographically distributed individuals.

Astroturfing techniques usually consist of a few people discreetly posing as mass numbers of activists advocating a specific cause. Supporters or employees will manipulate the degree of interest through letters to the editor, e-mails, blog posts, crossposts, trackbacks, etc. They are instructed on what to say, how to say it, where to send it, and how to make it appear that their indignation, appreciation, joy, or hate is entirely spontaneous and independent; thus being "real" emotions and concerns rather than the product of an orchestrated campaign. Local newspapers are often victims of astroturfing, by publishing letters that are identical to letters other newspapers have received.