Developments in the phenomenology of two-to-three particle reactions

Recent progress in understanding data on two to three particle hadron reactions is described. The use of an s-channel azimuthal angle selection is advocated to identify the separate different exchange mechanisms which contribute to the same final state at low subenergy. Solutions to the neutral Q cross-over problem in the Deck model are discussed, and experimental tests are proposed. Methods are offered for enchancing resonance signals in the presence of a large Deck exchange background. The need for absorptive corrections to the usual Deck model is stressed in the light of new FNAL data on diffractive neutron dissociation and ISR data on proton dissociation. Results of an explicit absobed pion exchange Deck model calculation are compared with data. (author)