The Art and Science of Interstellar Message Composition: Special Section Introduction by Douglas A. Vakoch Framing interstellar messages as art projects is a recent development. The Search for Extraterrestrial Intellligence, or SETI, has been conducted by scientists and engineers, with minimal input from the artistic community. With advances in search technology, the chances of detecting extraterrestrial intelligence are improving rapidly (see Werthimer and Morris’s abstract below). In recognition of these increasing prospects of success, the SETI Institute and Leonardo/The International Society for the Arts, Sciences and Technology (ISAST) have initiated a series of workshops to encourage discussion between artists, scientists, and technologists about interstellar message composition. In the event of a signal detection, this advance preparation will be especially useful as humankind decides whether to reply, and if so, what to say. This special section of Leonardo includes abstracts of six of the eighteen presentations given at the first workshop devoted specifically to the interface of art, science, and technology in interstellar message design, held in Paris on March 18, 2002. Interstellar messages have not typically been construed as works of art themselves, but art and music have played a minor role in the theory and practice of interstellar message construction. For example, German astronomer Sebastian von Hoerner has suggested that some aspects of music may be universal [1], and two Voyager spacecraft included samples of Earth’s music [2]. Indeed, the intrinsic temporality of radio transmissions lends itself particularly well to messages that share some of the structural characteristics of music. This approach to message design, based on semiotic analyses, suggests that the form of the transmission can help convey a message’s content [3]. Such a strategy stands in contrast to traditional methods of constructing interstellar messages based on classical information theory, in which there need not be a close connection between the form and content of a message. Although the 2002 Paris workshop was the first meeting to focus on the interface of art, science, and technology, a workshop held in Toulouse just months before also included artists’ perspectives to a limited extent, as reported at the Paris meeting by Italian philosopher Paolo Musso. At the Toulouse meeting, which covered interstellar message design more broadly, French artist Jean-Marc Philippe reviewed his project of transmitting an archive of messages from the Nançay radio telescope in 1987, and American artist Richard Clar examined the value of ambiguity and absence in interstellar messages. (See also Clar’s abstract below from the Paris workshop.) Several papers presented at the subsequent workshop in Paris examined whether there might be aesthetic principles that would be either universal or, lacking that, potentially explicable across interstellar space, even if these principles are culturally contingent. In several cases, mathematics and physics were suggested as possible bridges between worlds, with interstellar languages based on these disciplines potentially also capable of expressing aesthetic sensibilities across interstellar space. For example, American physicist Lui Lam suggested sending messages based on the Sierpinski gasket,