One side of the great contact equation between humans and extraterrestrials is already known: SETI is a human enterprise, so any success of a first contact depends on the compatibility between the human and extraterrestrial condition in interplay with contact parameters. Perceiving of, communicating with, and eventually understanding extraterrestrials are psychological matters. Moreover, regardless of the probability of a factual first contact, fictional extraterrestrials have already arrived on Earth: Myriads of cultural representations and scientific articles have dimmed or exited our expectations of a first contact. Research on how we think extraterrestrials and the plausibility of assumption is a task for the emerging field of exopsychology. We define this psychological field spanning the topics from theoretical considerations about the psychological properties of hypothetical interstellar neighbors to empirical work on human conceptions of extraterrestrials. Accordingly, we present the central premises of exopsychology and report the results of an empirical study (N=75) where participants rated 54 different cinematic portrayals of extraterrestrials regarding a multidimensional instrument addressing several key variables of exopsychology. The main focus of this empirical study was to predict trustworthiness which is pivotal for allowing personal contact with others. We revealed that psychological similarity with humans is more important than physical similarity. Furthermore, aggressiveness showed a strong negative and liking a strong positive effect on trustworthiness, while intelligence ratings played a subordinate role. How we think about extraterrestrials will carve out a corridor of possible first contact scenarios. Exopsychology strives for an improved understanding of the extraterrestrial mind and the human perspective. By identifying the necessary psychological requirements for producing techno-signatures, exopsychology can help specify and identify signs of extraterrestrial entities.