A number of commercially available ionomers are discussed. These include Surlyns, Nafions, and Thermoplastic Elastomers based on sulfonated rubbery backbones. In addition, a number of experimental ionomers described in the literature are examined, including those with semi-crystalline, elastomeric, and plastic backbones. Finally, the synthesis and some properties of a new class of end-functionalized ionomers, known as halato-telechelics are described. It is postulated that the properties of all these various classes of ionomers can be understood on the basis of a morphological model in which the salt groups aggregate to form physical crosslinks and microphase separated ionic clusters.