Dance is a universal human behavior and a crucial component of human musicality. When and how does the motivation and tendency to move to music develop? How does this behavior change as a process of maturation and learning? We characterize infants' earliest dance behavior, leveraging parents' extensive at-home observations of their children. Parents of infants aged 0-24 months (N = 278, 82.7% White, 84.5% in the United States, 46.0% of household incomes [greater than or equal to]$100,000) were surveyed regarding their child's current and earliest dance behavior (movement by the child, during music, that the parent considered dance), motor development, and their own infant-directed dance. We found that dance begins early: 90% of infants produced recognizable dance by 12.8 months, and the age of onset was not solely a function of motor development. Infants who produced dance did so often, on average almost every day. We also found that dance shows qualitative developmental change over the first 2 years, rather than remaining stable. With motor development, age, and more time dancing, infants used a greater variety of movements in dance, and began to incorporate learned, imitated gestures (80% of infants by 17.9 months). 99.8% of parents reported dancing for or with their infants, raising questions about the role of infant-directed dance. These findings provide evidence that the motivation and tendency to move to music appears extremely early and that both learning and maturation lead to qualitative change in dance behavior during the first 2 years, informing broad questions about the origins of human musicality.