Molecular epidemiology of rotaviruses emerged a little over 25 years ago as a fascinating branch of science that utilized then cutting-edge technology of RNA polyacrylamide gel electrophoresis. Molecular epidemiology, as I have observed it closely almost since its dawn, is an ever-evolving discipline which has incorporated the advances of the related sciences including molecular evolutionary biology and ecology, while it is firmly and deeply rooted in the edifice of epidemiology of infectious diseases. Rotavirus is a non-enveloped virus possessing 11 segments of double-stranded RNA as the genome and belongs to the Reoviridae family. The consequences of rotavirus infections in terms of mortality are different depending on whether children live in the developing countries or they live in the developed countries, and this difference comes mostly from the availability of proper medical intervention. A second generation rotavirus vaccine has just been licensed in Mexico and will hopefully be used widely among countries where the burden of the disease is the highest. One potential threat to the existing and future rotavirus vaccines is the extreme diversity of strains circulating among children across the world, and it is the key to understand how rotaviruses maintain themselves in nature. Molecular epidemiology of rotaviruses helps address such questions and has demystified the way in which they evolve including interspecies transmission of rotaviruses. A few examples are provided from the work that my colleagues and I did over the course of my career in an attempt to give a feel of molecular epidemiology of rotaviruses.