In this chapter, I explore how the study of grammatical gender has been a prime example of the impact that boundary crossing can have on the understanding of a phenomenon by creating nuance through the incorporation and juxtaposition of multiple perspectives. In the first section, I start with a description of grammatical gender and its different instantiations (or absence) across languages, including cue patterns, agreement structures, and noun-class parallels. I then move on to the ways in which grammatical gender has been investigated and how this research has crossed theoretical and methodological boundaries. The third section focuses on grammatical gender in SLA and aims to deconstruct the boundary between theory and practice, with a focus on what functional approaches have taught us about instruction of grammatical gender. The fourth section focuses on the history of grammatical gender instruction and the various pedagogies that have been tested to support the teaching of grammatical gender, including innovative approaches based on functional and sociocultural approaches. In the final section, I reflect on the many boundaries crossed: theoretical, methodological, disciplinary, linguistic, developmental, typological and, maybe most importantly, temporal. I end with a discussion of the future boundaries to be crossed in this area of research. [For the complete volume, "Crossing Boundaries in Researching, Understanding, and Improving Language Education: Essays in Honor of G. Richard Tucker. Educational Linguistics. Volume 58," see ED672546.]