Phenology is the study of the timing of recurring biological phases, the causes of their timing with regard to biotic and abiotic forces, and the interrelation among phases of same or different species.  Although phenology is a far-reaching component of environmental science, it is poorly understood relative to other ecological patterns and processes.  For example, it is unclear how environmental factors affect the phenology of different organisms, and how those factors vary in importance on different spatial and temporal scales. Futher, it is likely that phenology affects the abundance and diversity of organisms, and their function and interactions in the environment, especially their effects on fluxes in water, energy, and chemical elements at various scales. With sufficient observations and understanding, phenology can be used as a predictor for other processes and variables of importance at local to global scales, and could drive a variety of ecological forecast models with both scientific and practical applications.  The USA National Phenology Network (NPN) is a new data resource – a national network of integrated phenological observations essential to evaluate ongoing environmental changes (www.usanpn.org). The NPN will integrate with other observation networks and remote sensing products, emerging technologies and data management capabilities, and will capitalize on myriad educational opportunities and a new readiness of the public to participate in investigations of nature on a national scale.  We illustrate how phenology can be considered an integrative science for assessment of global change impacts, and for increasing awareness of citizens in terms of environmental impacts of human activities.