Thanks to their flexibility and intuitive programming model, spreadsheets are widely used in industry, often for businesscritical applications. Similar to software developers, professional spreadsheet users demand support for maintaining and transferring their spreadsheets. In this paper, we first study the problems and information needs of professional spreadsheet users by means of a survey conducted at a large financial company. Based on these needs, we then present an approach that extracts this information from spreadsheets and presents it in a compact and easy to understand way, using leveled dataflow diagrams. Our approach comes with three different views on the dataflow and allows the user to analyze the dataflow diagrams in a top-down fashion also using slicing techniques. To evaluate the usefulness of the proposed approach, we conducted a series of interviews as well as nine case studies in an industrial setting. The results of the evaluation clearly indicate the demand for and usefulness of our approach in ease the understanding of spreadsheets.