The number of males and females in a population affects both individual reproductive options and how members of the same and opposite-sex interact. Therefore, the adult sex ratio (ASR) is being increasingly recognized as a key demographic variable driving mating system evolution, parental investment, and mating competition. Traditional approaches towards understanding reproductive decision making in the social and biological sciences have focused on relatively rigid sex-determined roles and behavior, but more recent work has drawn attention to facultative shifts in reproductive strategies based on partner availability. During this workshop we will critically evaluate and synthesize ASR research to guide future work on reproductive strategies. Additionally, by better understanding the causes and consequences of ASR variation we hope to assist policy applications related to conservation biology, public health, violence, and sex-biased mortality and migration.