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Two-electron ions are of particular interest as they represent the simplest multi-electron system. Investigations of these ions along the isoelectronic sequence probe uniquely our understanding of correlation, relativistic, and quantum electrodynamical effects. Very recently, the theoretical and experimental investigations of these fundamental systems achieved a considerable improvement in accuracy. For the ground state the progress is in particular impressive, since even the two-electron QED effects can now be calculated with high precision. Experimentally, the progress achieved manifests itself by a novel approach , to the first time introduced in an experiment conducted at the Super-EBIT in Livermore. This technique allows to isolate the two-electron contributions to the binding energies in He-like ions. |