A thin elastic sheet wrinkles to avoid compression. When the compression is uniaxial the wrinkling direction is clear, and the main challenge is to understand its local length scale. When the compression is biaxial the situation is more complex, since even the direction of the wrinkling is hard to predict. Another important case is when the compression is due to geometric incompatibility, for example when a flat sheet is wrapped around a sphere or a curved shell is flattened by placing it on water. I will discuss some problems of this type, including dramatic recent progress by Ian Tobasco on wrinkling due to geometric incompatibility in a regime involving "asymptotic isometry."