the classical problem of counting elliptic curves with a rational n-isogeny can be phrased in terms of counting rational points on certain moduli stacks of elliptic curves. counting points on stacks poses various challenges, and i will discuss these along with a few ways to overcome them. i will also talk about the theory of heights on stacks developed in recent work of ellenberg, satriano and zureick-brown and use it to count elliptic curves with an $n$-isogeny for certain $n$. the talk assumes no prior knowledge of stacks and is based on joint work with brandon boggess.