Lectures on Applied $\mathrm{\ell }$-adic Cohomology

We describe how a systematic use the deep methods from $\mathrm{\ell }$-adic cohomology pioneered by Grothendieck and Deligne and further developed by Katz, Laumon allow to make progress on various classical questions from analytic number theory. This text is an extended version of a series of lectures given by the third and fourth authors during the 2016 Arizona Winter School.