In this work, we conducted a comprehensive investigation of ionpair interactions in the context of phase-transfer catalysis. We aimed to establish a thorough understanding of the nature and implications of these interactions. Our study began with the examination of pure ionic compounds to define the concept of an ion-pair in phase-transfer catalysis. We then explored a diverse range of ion-pair catalyst models to gain insight into the factors governing their interactions. Finally, we focused on the characterisation of real PTCs, providing crucial insight on the behaviour of these systems for real applications.