Sets of permutations play an important role in the design of some efficient algorithms. In this paper we design two algorithms that manipulate sets of permutations. Both algorithms, each solving a different problem, use fast matrix multiplication techniques to achieve a significant improvement in the running time over the naive solutions.For a set of permutations P ⊂ S n we say that i k-dominates j if the number of permutations π ∈ P for which π(i) < π(j) is k. The dominance matrix of P is the n × n matrix D P where D P (i, j) = k if and only if i k-dominates j. We give an efficient algorithm for computing D P using fast rectangular matrix multiplication. In particular, when |P | = n our algorithm runs in O(n 2.684 ) time. Computing the dominance matrix of permutations is computationally equivalent to the dominance problem in computational geometry. Thus, our algorithm slightly improves upon a well-known O(n 2.688 ) time algorithm of Matousek for the dominance problem. Permutation dominance is used, together with several other ingredients, to obtain a truly sub-cubic algorithm for the All Pairs Shortest Paths (APSP) problem in real-weighted directed graphs, where the number of distinct weights emanating from each vertex is O(n 0.338 ). A special case of this algorithm implies an O(n 2.842 ) time algorithm for real vertexweighted APSP, which slightly improves a recent result of Chan .A set of permutations P ⊂ S n is fully expanding if the product of any two elements of P yields a distinct permutation. Stated otherwise, |P 2 | = |P | 2 where P 2 ⊂ S n is the set of products of two elements of P . We present a randomized algorithm that computes |P 2 | and hence decides if P is fully expanding. The algorithm also produces a table that, for any σ 1 , σ 2 , σ 3 , σ 4 ∈ P , answers the query σ 1 σ 2 = σ 3 σ 4 inÕ(1) time. The algorithm uses, among other ingredients, a combination of fast matrix multiplication and polynomial identity testing. In particular, for |P | = n our algorithm runs in O(n ω ) time where ω < 2.376 is the matrix multiplication *