Growth and expansion in algebraic groups over finite fields

This is a brief introduction to the study of growth in groups of Lie type, with $S{L}_2({\mathbb{F}}_q)$ and some of its subgroups as the key examples. They are an edited version of the notes I distributed at the Arizona Winter School in 2016. Those notes were, in turn, based in part on my survey in Bull. Am. Math. Soc. (2015) and in part on the notes for courses I gave on the subject in Cusco (AGRA) and G"ottingen.