Models of ionic polymer metal composite transduction are described in this chapter, starting form black-box models, proposed during the infancy of this technology, to arrive to grey-box and white-box models, capable of providing a significant contribution to the understanding of the involved phenomena. A continuous comparison among the models proposed by various authors is given to show the constant influences and evolution of the addressed topic. The role of experimental validation is outlined, along with the theoretical results, as a main step towards the validation of the proposed transduction models.