This disputatio is an inquiry into the nature of the truly human sexual act. The authors first present and critique the types of complementarity—heterogenital, reproductive, communion, affective, and parental—that the magisterium finds in a truly human sexual act. They then suggest that heterosexual or homosexual orientation as part of a person’s sexual constitution requires adding orientation complementarity to the equation. This addition yields the conclusion that holistic complementarity—an integration of orientation, personal, and biological complementarities—is a more adequate sine qua non of truly human sexual acts.