Contents 1. Introduction 2. Historical perspective and previous reviews 3. Theoretical and computational results 3.1 Single ions 3.1.1 Clusters 3.1.2 Extended interfaces 3.2 Finite ion concentrations and counterion effects 4 Experimental studies and comparison with simulation results 4.1 Surface tension 4.2 Surface potentials 4.3 Heterogeneous chemical processes 4.4 Photoelectron spectroscopy 4.5 Surface selective nonlinear spectroscopies 5 Future developments 6 Conclusions