  This is a survey on problems involving equations $-\operatorname{div}{\Cal
A}(x,\nabla u)=\mu$, where $\mu$ is a Radon measure and ${\Cal A}:\bold
{R}^n\times\bold R^n\to \bold R^n$ verifies Leray-Lions type conditions. We
shall discuss a potential theoretic approach when the measure is nonnegative.
Existence and uniqueness, and different concepts of solutions are discussed for
general signed measures.
