Many leading Internet dating sites claim to be able to find compatible matches for singles, and that they use principles from Relationship Science to generate their matching algorithms. In this article, I first discuss how ―relationship compatibility‖ has been studied in Relationship Science. It is generally not directly studied, but inferred from related constructs, including satisfaction, commitment, and endurance of the relationship. Second, I discuss three principles that are referred to in Relationship Science as defining a pair being a ―compatible match.‖ These principles are similarity, complementarity, and matching (on same level of socially desirable characteristics, regardless of whether they are the same or different between partners). In the final section, I discuss what aspects of science are being used at the Internet dating sites to create compatible matches.