It is well established that a variety of environmental factors affect sexual development, sexual phenotype, and reproductive function. In fishes, the focus of much of my research, these environmental effects are often pronounced, readily perturbed or manipulated, and thus amiable for study. Among the most striking of these phenomena is the complete female to male sex change during adulthood that occurs in some fishes due to changes in their social environment. Typically, the absence of a dominant male triggers sex change in the dominant female. How male absence initiates such a striking transformation is as mysterious as it is extraordinary. Social position is clearly important, but the behavioural and other cues a female employs to determine her position in the hierarchy and how that influences her decision to change sex or defer to others remain unknown. Here, I will highlight work from my lab that is revealing the behavioural, genetic, epigenetic and physiological underpinnings that enable socially controlled sex change in fish.