There is increasing evidence that gap junctional communication plays an important role in the control of morphogenesis, differentiation and growth. Here we review the genetic diversity of connexins, structural proteins which form the gap junction, with emphasis on their tissue specific expression and present evidence that junctional communication is perturbed during the process of carcinogenesis. Finally we discuss the clinical implications of these findings in the light of recent experiments demonstrating that increased junctional communication, achieved by pharmacological or by molecular means, results in suppression of tumorigenicity or in enhanced growth control.