This book discusses the potential roles of miRNA as a crucial regulator in cancer biology. It examines the regulation of drug resistance by miRNAs in cancers and the mechanism of their deregulated expression. The book discusses the role and molecular mechanism of miRNA in regulating cellular proliferation and cell cycle. It analyses circulating miRNAs as biomarkers for cancer diagnosis and prognosis. It also analyzes the role of miRNA as a modulator of the development and function of tumor-associated immune cells. It explores the cross-talk between miRNA and reactive oxygen species (ROS) in pathogenesis, cancer therapeutic tolerance, and resistance. It provides insights into the role of miRNA in cancer angiogenesis, metastasis and describes strategies and associated challenges of miRNA-based therapies.