The aim of this special collection is to present recent progress made, and reflect current ideas, in research fields where positron and positronium are involved. The contents cover a wide range of positron-related research topics; including both fundamental (theoretical calculations, radiation chemistry, hyperfine interactions, positronium physics and chemistry) and applied (metal, polymer, thin film and other materials, development of experimental techniques) aspects. This will be of especial interest to anyone planning to use such techniques.