MicroRNAs (miRNAs) are an evolutionarily conserved class of small regulatory RNAs that modulate gene expression. Extensive research over the last decade has shown that miRNAs are master regulators of cellular processes, with an essential role in cancer initiation, progression, and metastasis. Widespread deregulation of miRNAs in cancers has identified oncogenic and tumor-suppressive roles for these miRNAs. On the basis of these observations, miRNAs have emerged as promising therapeutic tools for cancer management. In this review, we focus on the roles of miRNAs in tumorigenesis, the rationale and strategies for the use of miRNA-based therapy for cancer, and the advantages and current challenges to their use.