This article deals with the process of identity transmission in situations of culturally mixed unions. As children of such unions question their belonging and identity, what choices do parents make for transmitting identity? Looking at franco-maghrebi couples living in the suburbs of Paris, we will expose the various questions and occasional conflicts that arise from their filiation. Marital and familial negotiations about identity transmission throw back upon the parents the “illegitimate” position in which they find themselves. We will explain how and why the term of “marital illegitimacy” may be used to describe these couples. We will then explore various examples of transmission choices in which the “illegitimate” situation of the couple notably transpires.