Lawesson reagent for selenium fans: Phosphorus selenium heterocycles and, in particular, [PhPSe(2)](2) (known as Woollins' reagent) are proving valuable in the synthesis of new heterocycles and for the insertion of selenium into organic substrates. Incorporation of phosphorus and selenium atoms into the products leads to a surprising variety of structures.Phosphorus-selenium ring chemistry has developed to include the synthesis of some exciting new motifs and provided organic chemists with a new reagent, [PhPSe(2)](2), which has become known as Woollins' reagent.