Complexity theory typically studies the complexity of computing a function h(x) : {0, 1}n → {0, 1}m of a given input x. We advocate the study of the complexity of generating the distribution h(x) for uniform x, given random bits. Our main results are: • There are explicit AC circuits of size poly(n) and depth O(1) whose output distribution has statistical distance 1/2n from the distribution (X,...