Theory and research have a reciprocal relationship. Prevailing theoretical approaches fall out of fit as societies change and fresh approaches are called for. In this chapter, it is argued that we need to reflect critically on the binary cisgendered approaches that have been fundamental to gender and health research since its inception. It is critical to acknowledge that gender binarism is a powerful force within societies globally and that it exerts a significant influence upon health and health practices. But, at the same time, gender is becoming increasingly complex and multifaceted. A case is made for exploring gender binarism and gender multiplicity as co-constitutive of health, as intrinsically relational, and as finding expression in social structures, practices, and experiences that promote advantages for some and disadvantages for others. To achieve this, it is proposed that we need to make use of theoretical tools which reach beyond gender as a standalone concept by taking an intersectional approach which directs analysis ‘upstream’ to the health consequences of intersections between power structures and systems of oppression for different genders.