1. A computer-implemented method for assigning Access Control Lists (‘ACLs’) to a hierarchical namespace to optimize ACL inheritance, the method comprising: creating, by a computer processor, an entitlement matrix for a plurality of resources; creating, by the computer processor, a tree structure having a plurality of nodes for the hierarchical namespace in dependence upon the entitlement matrix; creating, by the computer processor, a plurality of ACLs in dependence upon the entitlement matrix, wherein each ACL includes permissions that a user or group has to a specific system ebb; identifying, by the computer processor, a plurality of attachment points in the hierarchical namespace for the ACLs in dependence upon ACL attachment rules, including determining a most popular ACL, wherein no other ACL represents more nodes in the tree structure than the most popular ACL; and attaching, by the computer processor, the ACLs to the attachment points.