This presentation will focus on answering two questions; why do we see biased sex ratios in dioecious plant populations, and why does dioecy evolve at all? To address the first question, sex ratio theory was used in conjunction with the analysis of over 200 studies from the literature. Species were categorized based on their life form, pollination agent, fruit dispersal agent, and sex ratio. A loglinear analysis was used to look at possible correlations between the sex ratio of a population and other life history characteristics. Despite the limited sample size, strong relationships are observed. 93% (13 of 14) of insect pollinated vines with biotically dispersed fruit have male-biased sex ratios. Conversely, 61% (11 of 18) of wind pollinated shrubs with abiotically dispersed fruit have female-biased sex ratios. To address the second question we developed two complimentary models that incorporate multiple variables and their interactions. We examined the effects of inbreeding depression, consanguineous mating, compensation, and specialization on unisexual invasibility in a hermaphrodite population. Two key results are that it is the interaction effects of multiple variables that allows for unisexual invasion at thresholds witnessed in nature, and mating among relatives has the ability to significantly enhance the invasibility of a unisexual mutant into a population if inbreeding depression is sufficient.