Can professional cultures contribute to wage inequality? Recent literature has demonstrated how widely held cultural biases reproduce ascriptive inequalities in the workforce, but cultural belief systems "within" professions have largely been ignored as mechanisms of intra-profession inequality. I argue that cultural ideologies about professional work, which may seem benign and have little salience outside of a profession's boundaries, play an important role in reproducing wage inequalities therein. Using nationally representative data on engineers, I demonstrate that patterns of sex segregation and gendered wage allocation in engineering break consistently along the lines predicted by its "technical/social dualism"--an ideological distinction between "technical" and "social" engineering subfields and work activities. After explaining how these findings deepen our understanding of gender inequality in engineering, the article discusses how the consideration of professional cultures may open up fresh areas of inquiry into intra-profession inequality more generally.