This chapter covers the principles of data visualization, emphasizing the importance of graphs in communicating data insights. It discusses basic principles such as simplicity, clarity, and avoiding repetition, as well as pre-attentive processing and visual design principles such as the rule of thirds and the Z-pattern of scanning. The chapter also critiques common types of graphs such as pie charts and 3D plots, and introduces binned scatterplots. It concludes with guidelines on communicating graphs effectively and designing dashboards.