In a fast-moving field it is unlikely that articles written more than a year ago would be completely up to date. The purpose of this book is to bring to the nonspecialist an overall view as well as an update on the state of the art as it existed in the beginning of 1982, and to the specialist the opportunity to have a single source of information for how the other organisms do it, and also to enable him to find out the status of the various aspects of RNA processing with which he might not be to familiar. even if only some of these goals are achieved, all those who labored so diligently to bring about the publication of this book would be more than gratified.