This document introduces Processing, an open-source data visualization tool. It discusses Processing from three perspectives: as a language, an integrated development environment (IDE), and a community. As a language, Processing is Java-based and can be used to create graphics, handle input/output, and perform calculations. The IDE allows Processing sketches to be developed and run. Finally, the community develops libraries and shares resources that expand Processing's capabilities, such as map visualization and handling of different data sources.