MicroRNAs are endogenous, highly conserved, tiny noncoding RNA chains of 21–24 nucleotide sequences. They play central function in posttranscriptional regulation of gene by targeting mRNAs. Generally, a wide range of cellular processes such as cell cycle regulation, differentiation, cell stress response, and apoptosis are under the control of miRNAs due to their regulatory mechanisms. Studies have revealed that some events such as mutation in miRNA genes, defects in miRNA processing, and dysregulation of miRNA may cause diverse human diseases including cancers. Under certain circumstances, miRNAs can act as oncogenes or tumor suppressor genes. The dysregulated miRNAs have been observed to affect the characteristics of cancer, including its proliferation, inhibition of programmed cell death, invasion, metastasis, and angiogenesis. miRNAs have garnered interest in recent years as potential diagnostic, prognostic, and therapeutic tools for a variety of human malignancies. This chapter highlights key aspects of miRNAs in context to cancer, covering the biogenesis of miRNAs and its dysregulation. Furthermore, the role of miRNAs in cancer metastasis and its potential as cancer biomarker are also discussed.