A voyage into the mysterious world of alien intelligence Do advanced life forms exist beyond Earth? Is there intelligent life elsewhere in the cosmos? Ask an astrobiologist and you will usually get back a qualified "yes," but further investigation is stymied by the slipperiness of concepts like "advanced" and "intelligent." Most astrobiologists then turn their attention to more tractable scientific issues, examining geological and biological conditions for life on Earth in order to propose how it might have arisen elsewhere. Their ambition is to understand life wherever it occurs as part of the processes of planetary formation and change. Gary Tomlinson extends this scientific project as only a humanist can. Starting from the foundation of earthly meaning, sign making or semiosis, he opens a new path toward the alluring question of alien intelligence. He joins evolutionary science, information theory, and a theory of the constraints under which signs occur to delimit the grounds for the emergence of meaning-making life forms anywhere. Astrosemiosis identifies evolved features on earth plausibly required to meet semiotic constraints and gauges the likelihood that analogous features would evolve in extraterrestrial biospheres. Rethinking sign making as a planetary process, it narrows the gap between speculation on smart aliens and empirical astrobiological science.