Infant sleep is an important aspect of infancy. Its influence extends into later years of child development and across various domains, including cognitive, emotional, and behavioral development. High-quality sleep in the first few years of life also lays the foundation for healthy sleep habits later on. Recent advances in technology have provided new opportunities and tools for collecting intensive longitudinal measurements of sleep quality in ways that are not intrusive to daily life. We are using dynamic system modeling techniques to analyze nighttime actigraphy (movement) data and explore reciprocal influences among the sleep/wake cycles of infants and parents. Between-family differences due to demographics (including infant/parents’ age, parents’ psychological health condition, etc.) and family environment variables (such as material satisfaction scores, household chaos scores, infant sleep arrangement, etc.) are also evaluated as part of this project