In human societies all over the world, adults form life-long emotional attachments, or pair bonds. In many societies and cultures, multiple bonded partnerships are encouraged or tolerated, which can take many forms (e.g. polygamy), and when adults form exclusive partnerships based on these pair bonds, relationship scientists refer to this as social monogamy. In both socially exclusive and non-exclusive arrangements, there are moral and ethical norms underlying the codes of conduct that people adopt for their relationships. Stemming from frameworks developed by evolutionary, socio-cultural, personality, and developmental theorists, we understand a great deal about the morals and ethics surrounding monogamy and non-monogamy in adult romantic relationships. This entry will discuss some of the highlights within this line of research.