Traditional notions of marriage have been the foundations for many families in contemporary Western culture. Philosopher Immanuel Kant, who attempted to create a unified system of ethics, believed that the only true way for sex to be moral is through a heterosexual, monogamous marriage union, blasting the notions of homosexuality and polygamy, among other types of sexual activities, as "unnatural." These views were presented in Kant's Metaphysics of Morals and Lecture on Ethics. But as time has passed, there has been an evolution of thought away from this point of view for many people. This thesis examines the possibility that polygamous, same-sex, and group marriages could fit into Kant's marriage right that was previously reserved only for heterosexual, monogamous marriage. Kant created a marriage right that allowed for moral sexual activity using the Categorical Imperative, most notably the "formula of humanity," as the basis for not objectifying sexual partners. The research examines area that the topic of marriage debate has been held, including biological and sociological journals, as well as philosophical journals which question the integrity of Kant's marriage right. I defend Kant's formation of the marriage right as it is presented since it focuses on the equality of partners in the marriage union. Acknowledging the marriage right and using the research, I present arguments against Kant's critiques of polygamous and same-sex marriage, claiming that these types of marriages are natural and they follow the guidelines that Kant establishes for the marriage right. I also examine the case of group marriage, which is not explicitly critiqued by Kant. I come to the conclusion that polygamous, same-sex, and group marriage could be moral on the grounds that Kant lays out in his marriage right and that he wrongly excluded them on the false premise of their being "unnatural."