The theory of non-linear evolutionary partial differential equations (PDEs) is of fundamental importance in mathematical analysis and through recent breakthroughs and insights it has reached a stage where some difficult and important questions can be fruitfully addressed. This program will focus on a large class of singular and degenerate PDEs ranging from flows by mean curvature to the infinity Laplacian. Although these equations have a common structure, they are connected to many different applications such as the diffusion in highly non-homogeneous media. A crucial role in understanding non-linear phenomena is played by regularity estimates based only on the structure of the equations. In several ways the recent advances open up a whole new area of research similar to the progress that started a few decades ago concerning regularity and free boundary problems for linear PDEs. The new methods have already turned out to be powerful enough to solve previously unreachable problems.