Chemistry of the Positron and of Positronium

In this progress report, the properties and behavior of the positron (“positive electron”, anti‐electron) and of the positronium, a “hydrogen atom” containing a positron instead of a proton, are considered from the chemist's viewpoint. Examples are given to demonstrate the development of positronium chemistry, in aqueous solution and in the gaseous, liquid, and solid phases, with its problems and possibilities.