MicroRNAs (miRNAs) are short non-coding RNAs of 20-24 nucleotides that play important roles incarcinogenesis. Accordingly, miRNAs control numerous cancer-relevant biological events such as cell proliferation,cell cycle control, metabolism and apoptosis. In this review, we summarize the current knowledge and conceptsconcerning the biogenesis of miRNAs, miRNA roles in cancer and their potential as biomarkers for cancerdiagnosis and prognosis including the regulation of key cancer-related pathways, such as cell cycle control andmiRNA dysregulation. Moreover, microRNA molecules are already receiving the attention of world researchersas therapeutic targets and agents. Therefore, in-depth knowledge of microRNAs has the potential not only toidentify their roles in cancer, but also to exploit them as potential biomarkers for cancer diagnosis and identifytherapeutic targets for new drug discovery.