A data flow diagram (DFD) is a graphical tool used to depict the flow of data in an information system. It shows external entities, processes, data stores, and data flows. DFDs are drawn at multiple levels of detail, with each level breaking down processes into more detail. The highest level context diagram shows the overall system as a single process. Lower level DFDs decompose processes into more detail through multiple levels. This document reviewed how to create DFDs, including rules, symbols, and conventions for naming and structuring multiple levels of detail.