This article considers what the implications of decertification would be for single-sex services such as domestic and sexual violence support. Some reform options attached to decertification could (re)allocate authority away from the state to organisations or individuals to determine gender criteria. What would the consequences of such re-allocation be in determining eligibility to receive or access services or excluding people on the basis of a characteristic protected under equality law? Engaging with this in the context of domestic and sexual violence (...) support service provision raises a number of questions. Firstly, does the existence of gender-based violence and/or of the effects it produces require a stable category in order to address them? What benefits may emerge from providing single-sex spaces that could not be replicated in other settings? And finally, what criteria of exclusion and inclusion are currently used to determine access to spaces beyond legal gender status? (shrink)