The Subject Of This Book Is The Action Of Permutation Groups On Sets Associated With Combinatorial Structures. Each Chapter Deals With A Particular Structure: Groups Geometries Designs Graphs And Maps Respectively. A Unifying Theme For The First Four Chapters Is The Construction Of Finite Simple Groups. In The Fifth Chapter A Theory Of Maps On Orientable Surfaces Is Developed Within A Combinatorial Framework. This Simplifies And Extends The Existing Literature In The Field. The Book Is Designed Both As A Course Text And As A Reference Book For Advanced Undergraduate And Graduate Students. A Feature Is The Set Of Carefully Constructed Projects Intended To Give The Reader A Deeper Understanding Of The Subject.