MicroRNAs are involved in crucial biological processes, including developmental timing, cell proliferation, apoptosis, and stress responses. This book presents topical research in the study of microRNAs, including their potential applications in aquaporin associated pathogenesis; microRNAs as novel biomarkers and therapeutic targets for cancer; microRNAs used in regulating EMT and blood circulation metastasis of lung cancer stem cells; the biological functions of microRNAs in animals and the regulation of metabolism, ageing and lifespan by microRNAs.