Reproductive success varies extensively within and among plants, often without pattern. Although such stochastic variation is often disregarded as noise that complicates understanding, it can significantly affect average reproductive output if performance during late reproductive stages depends nonlinearly on the success of earlier stages. For example, variation in pollen dispersal reduces expected female and male success if seed production decelerates with increasing pollen receipt, because less-than-average receipt diminishes mean seed production more than copious pollination increases it (Jensen窶冱 inequality). This lecture outlines the nature of variation in pollen dispersal, its distribution within and among plants, the role of animal pollination in creating variation, and some of the ecological and evolutionary consequences of variation during the reproductive process. Key findings include clarification of the possibility that seed production within populations can be pollen limited even though the average plant receives adequate pollen and an explanation for the rarity of separate sexes among plants, but not among animals.