In this chapter I’ll discuss how to control the overall appearance of graphics made by ggplot2. The grammar of graphics that underlies ggplot2 is concerned with how data is processed and displayed – it’s not concerned with things like fonts, background colors, and so on. When it comes to presenting your data, there’s a good chance that you’ll want to tune the appearance of these things. ggplot2’s theming system provides control over the appearance of non-data elements. I touched on the theme system in the previous chapter, and here I’ll explain a bit more about how it works.