Gender is an increasingly prominent filter in jazz research. Close inspection shows that even the presumably neutral territory of key signatures creates gendered reverberations. This chapter examines how replicating the “canonical” keys of jazz standards marginalizes female singers, who comprise the predominant sex of jazz vocalists. The argument is first contextualized through examining how canonical keys are set and perpetuated through jazz standards, jazz practice and fake books. These canonical keys, whilst mostly drawn from instrumental practice, generally accommodate male vocal range. The keys of 40 well-known standards recorded by renowned female vocalists were compared to printed keys in fake books. This comparison shows that keys recorded by female singers seldom match the printed keys. A discussion of jazz vocal style and function follows, to explain why singing in canonical keys can lead to jazz female singers’ marginalization, and why transposition to a suitable key is fundamental to achieving an authentic jazz vocal sound. The chapter concludes by outlining several implications of this analysis for jazz practice and education, particularly in relation to the developing female jazz singer. It recommends ways to foster inclusivity regarding female vocalists and key choice.