This book is the second volume in the Handbook of Surface Science series and deals with aspects of the electronic structure of surfaces as investigated by means of the experimental and theoretical methods of physics. The importance of understanding surface phenomena stems from the fact that for many physical and chemical phenomena, the surface plays a key role: in electronic, magnetic, and optical devices, in heterogenous catalysis, in epitaxial growth, and the application of protective coatings, for example. Therefore a better understanding and, ultimately, a predictive description of surface and interface properties is vital for the progress of modern technology. An investigation of surface electronic structure is also central to our understanding of all aspects of surfaces from a fundamental point of view. The chapters presented here review the goals achieved in the field and map out the challenges ahead, both in experiment and theory.