There are many properties of scintillators that are of importance for application. One property is the energy resolution for the detection of γ-rays, and during past 20 years we witnessed enormous progress. The state of the art resolution for the detection of 662 keV γ photons was 5–6% at the end of the 20th century, and today scintillators with 2.2% resolution are commercially available. This work will provide a review on the development of high resolution chloride, bromide, and iodide based scintillators that occurred since the discovery of the LaCl3:Ce3+ scintillator in 2000. Bandgap engineering and co-doping to eliminate afterglow or to improve proportionality have become new tools in optimizing scintillator performance. At the end of the review the prospects for the development of scintillators with resolution <2% are addressed together with new research strategies that might be required to accomplish that.