Non enveloped viruses constitute an important class of medically significant pathogens. They encode their proteins in single (ss) and double strand (ds) RNA and DNA genomes and display a variety of sizes and structures. In this volume experts in the field provide up to date descriptions of many characteristics associated with the ssRNA noda, picorna and calciviruses, the dsRNA reo and rotaviruses, the ssDNA parvoviruses and the dsDNA polyoma and adenoviruses. While many aspects of these viruses have been addressed previously, this volume specifically focuses on the issue of their entry into cells, with particular attention to the translocation of the viral genome through a membrane, without the aid of inter-membrane fusion that is common and reasonably well understood in enveloped viruses. Sufficient detail has been revealed in most of the viruses discussed in this volume to establish a credible argument for convergent evolution. A variety of mechanisms are described to generate and tightly control the exposure of a fusion-like peptide or an entire gene product that facilitates membrane permeation and genome delivery into the cytoplasm and, for the DNA viruses, the nucleus. Since there is no viral membrane to fuse with the cellular membrane, the events at this interface are different from those associated with enveloped viruses and with the various fusion events associated with normal cellular function. Thus, while the factors critical for this process to occur have been well established for many of these viruses, a specific mechanism for genome penetration is yet to be determined. We believe that this volume will provide a reference of enduring value for the non enveloped virus field and our hope is that the focus on entry and genome translocation across a cellular membrane will stimulate new ideas and mechanistic studies of this critically important process.