The presence of a trans* family member can challenge existing theoretical notions about the development of gender in families. Emerging knowledge about trans* identities consolidates around 5 primary challenges to existing theoretical notions of gender: (a) non-dimorphic sex, (b) nonbinary gender, (c) the biological and social construction of gender, (d) gender identity development, and (e) family meaning making about transgender identity. These challenges structure an examination of hetero- and cisnormative expectations within family theory and help unpack long-standing tensions between essentialist and social constructionist views of gender development. This can play out in family theory through a recognition of the tension between upholding and decentering cisnormativity within families. This article pinpoints locations where current family theories require reexamination and expansion to accurately conceptualize the flexibility and variability of families with trans* members.