Roadside Picnic (Russian: , Piknik na obochine, ) is a philosophical science fiction novel by Soviet-Russian authors Arkady and Boris Strugatsky, written in 1971 and published in 1972. It is the brothers' most popular and most widely translated novel outside the former Soviet Union. As of 2003, Boris Strugatsky counted 55 publications of Roadside Picnic in 22 countries. The story is published in English in a translation by Antonina W. Bouis. A preface to the first American edition was written by Theodore Sturgeon. Stanisław Lem wrote an afterword to the German edition of 1977. The book has been the source of many adaptations and other inspired works in a variety of media, including stage plays, video games, and television series. The 1979 film Stalker, directed by Andrei Tarkovsky, is loosely based on the novel, with a screenplay written by the Strugatsky brothers. The term stalker became a part of the Russian language and, according to the authors, became the most popular of their neologisms. In the book, stalkers are people who trespass into the forbidden area known as the Zone and steal its valuable extraterrestrial artifacts, which the stalkers sell. In Russian, after Tarkovsky's film, the term acquired the meaning of a guide who navigates forbidden or uncharted territories; later on, fans of industrial tourism, especially those visiting abandoned sites and ghost towns, were also called stalkers. Setting Roadside Picnic is set in the aftermath of an extraterrestrial event called the Visitation that simultaneously took place in several locations around the Earth over a two-day period. Neither the Visitors themselves nor their means of arrival or departure were ever seen by the local populations who lived inside the relatively small areas, each a few square kilometers, of the six Visitation Zones. The zones exhibit strange and dangerous phenomena not understood by humans, and contain artifacts with inexplicable properties. The title of the novel derives from an analogy proposed by the character Dr. Valentine Pilman, who compares the Visitation to a picnic: In this analogy, the nervous animals are the humans who venture forth after the Visitors have left, discovering items and anomalies that are ordinary to those who have discarded them, but incomprehensible or deadly to the earthlings. This explanation implies that the Visitors may not have paid any attention to, or even noticed, the human inhabitants of the planet during their visit, just as humans do not notice or