Regular and chiral polytopes in low dimensions
  There are two main thrusts in the theory of regular and chiral polytopes: the abstract, purely combinatorial aspect, and the geometric one of realizations. This brief survey concentrates on the latter. The dimension of a faithful realization of a finite abstract regular polytope in some euclidean space is no smaller than its rank, while that of a chiral polytope must strictly exceed the rank. There are similar restrictions on the dimensions of realizations of regular and chiral apeirotopes. From the viewpoint of realizations in a fixed dimension, the problems are now completely solved in up to three dimensions, while considerable progress has been made on the classification in four dimensions, the finite regular case again having been solved. This article reports on what has been done already, and what might be expected in the near future. 
Peter McMullen (University College London), Egon Schulte (Northeastern   University)