Differences between men's and women's voices are frequently attributed to physiological differences between the sexes. However, ample linguistic literature has shown that many of these distinctions are in fact socially learned (see Simpson 2009 for a review). One particularly strong piece of evidence for the social nature of the gendered voice comes from the literature on childhood language socialization, which shows that boys and girls taken on gender-appropriate phonetic traits long before physiological differentiation occurs (e.g. Sachs et al. 1973). Even features linked to biology -such as vocal pitch -differ across cultures, as can be seen in work like Yuasa's (2009) treatment of the pitch in American English and Japanese. However, we still lack a comprehensive understanding of a number of issues, among them: which phonetic features are influenced by biology, and how strong is this influence? Which are learned as part of language socialization? Finally, how malleable are these features beyond childhood?I take steps toward addressing these questions by focusing on a group that is almost completely absent from the linguistic literature: female-to-male transsexuals, or trans men. Trans men are individuals who are assigned to a female gender role at birth and raised accordingly, but who come to identify as men and take steps to transition from a female gender role to a male one. Previous studies of transsexuals' voices have shown that we can learn quite a bit from looking at speakers who cross the gender divide, though the focus has generally been on trans women (i.e. male-to-female transsexuals). For instance, Gelfer and Schofield (2000) analyzed the differences between trans women whose voices were perceived as male and those perceived as female and identified 160 Hz as a cross-over point that distinguished the two groups. Trans men, on the other hand, promise a unique set of insights for a number of reasons. First, one of the most common medical interventions sought by trans men is testosterone therapy, which produces many of the physiological changes men typically experience during puberty, including a marked drop in vocal pitch that usually results in a male-sounding voice. Second, in addition to shedding light on gender differences in the voice, trans men also show how different kinds of masculinity are perceived, as my work on gay-sounding voices among trans and non-trans men has shown (discussed below). Finally, trans men underscore the importance of viewing masculinity as a social achievement. As Kulick (1999) notes, it is all too easy to assume that trans women are actively constructing their femininity while treating trans men as if they are doing nothing in particular by accomplishing masculinity. In other words, the near-exclusive focus on trans women over trans men reinforces the unmarked status of male speech.In this paper I discuss two analyses I have done as part of an on-going investigation of the properties of trans men's voices. The first of these, which sheds light on the role of language s...