Data assimilation, the fusion of observations with model forecasts, is one of the most important and challenging aspects of prediction of our earth system, including the atmosphere, ocean, land, sea ice, and etc. Sophisticated data assimilation algorithms that combine ingredients from numerical modeling, observational studies, statistics, and dynamics of the earth system, have been developed at operational centers around the world. Exciting new data assimilation algorithms that aim to better understand the earth system are also being developed. This one-week summer school will bring together experts from leading prediction centers and researchers from top institutes and universities. A broad overview of statistics fundamentals, widely applied data assimilation methods including the ensemble Kalman filter and variational methods, and advanced data assimilation approaches, such as ensemble smoothers, non-Gaussian filters and particle filters, will be introduced. Applications of advanced data assimilation in geosciences, including oil reservoir and sea ice, and radiance data assimilation, will also be presented. Finally, topics on the frontier of data assimilation integrated with machine learning will be discussed.