The generally accepted mechanism for nucleophile arylation with diaryliodonium salts via ipsosubstitution of I(III) involves reversible ligand substitution on iodine followed by rate determining ligand coupling (Scheme 1b). This mechanism is based on kinetic analysis of some of the earliest phenylation reactions with diphenyliodonium chloride. However, reactions of diaryliodonium salts have evolved significantly in the past 75 years such that modern reactions of diaryliodonium salts no longer resemble those that were used to establish the mechanism. For instance, halides, which were common counter anions in the past, have been replaced by "non-coordinating" anions such as triflate and tetrafluoroborate; identification of aryl "dummy" ligands has led to chemoselective reactions of unsymmetrical diaryliodonium salts; and finally, the vast majority of reactions are conducted in organic solvents such as toluene, dichloromethane, or acetonitrile and not water or water-solvent mixtures. Moreover, although recent efforts to understand the mechanism of ligand coupling with diaryliodonium salts have focused on DFT analysis, there have been no updated kinetic studies since the seminal work of Beringer (ca. 1955). Kinetic studies of palladium catalysed reactions have been instrumental to a deeper understanding of the fundamental interactions and for advancing new synthetic methods. Here, we address unanswered questions in modern reactions of diaryliodonium salts, such as the kinetic significance of the counter anion and the aryl auxiliary and the role of frontier orbitals in coordination number and geometry of iodine in kinetically relevant steps (Scheme 1b).