Combinatorics in general and the theory of expander graphs, in particular, have been fruitful areas of  interaction of pure and applied mathematics. In recent years a "high dimensional" theory has been emerged. This theory beside its intellectual interest has also a great potential for various applications in mathematics and computer science. This theory calls for a cooperation of experts in combinatorics, topology, geometry, group theory and computer science. We propose to organize a program that will bring together people from these areas in order to create a community of scholars who can cooperate on these new challenges.