 The paper discusses the potential of data assimilation, DA, in improving hydrologic predictions, but notes that advances in research have not been adequately implemented in operational forecast systems due to challenges such as quantifying uncertainty and efficiently merging data and models. A hydrologic DA workshop was held in Delft, Netherlands in 2010, which led to a review of the current status of DA applications in both research and operations, and discussion of potential hurdles and opportunities for transitioning research into cost-effective operational forecasting tools. The paper covers several related aspects, including theoretical aspects in DA algorithms, uncertainty estimation, new observations, real-time control of water resources systems, and community-based, generic DA tools. It recommends that cost-effective transition from research to operations should be facilitated by developing community-based, generic modeling in DA tools or frameworks, and fostering collaborative efforts among hydrologic modelers, DA developers, and operational forecasters. This article was authored by Y. Lu, A. H. Wirtz, and Clark, and others. We are article.tv, links in the description below.