Abstract
This first chapter of the book aims to provide readers the basic information necessary for better understanding the contents of other chapters. The chapter begins with the stories or history of discovery of miRNAs. From this section, readers can get a sense on how some groundbreaking scientific findings could be achieved from small but mysterious things. In the second section, the whole pathway of biogenesis of miRNAs is described in detail, from transcription to maturation. This is followed by the section on action of miRNAs describing how mature miRNAs are hooked up to the protein complex and guide the complex to target genes to execute repression of gene expression at the post-transcriptional level. Finally, some important issues related to miRNA function are introduced in the section entitled “Some conceptual notes about miRNA function.”