Given a group G acting on a set X, an element g of G is called a derangement if it acts without fixed points on X. The Boston--Shalev conjecture, proved by Fulman and Guralnick, asserts that in a finite simple group G acting transitively on X, the proportion of derangements is at least some absolute constant c > 0. We will first give an introduction to the subject, highlighting some connections with number theory. Then, we will see a version of this conjecture for the proportion of *conjugacy classes* containing derangements in finite groups of Lie type. Joint work with Sean Eberhard.