MicroRNAs (miRNA) have emerged as critical player in the field of life sciences. These are endogenously expressed small non coding RNAs that function to control post-transcriptional gene expression. These small RNAs have been shown to regulate the cell growth, differentiation and apoptosis. miRNAs regulate messenger RNA expression by targeting homologous sequences in mRNAs and further regulate the expression of endogenous genes either by mRNA cleavage or translational repression. One miRNA is capable of regulating several distinct mRNAs and are believed to modulate more than one-third of the mRNA species encoded in the human genome. In this review, biogenesis of miRNAs and their regulatory mechanism is addressed. Moreover, the potential application of miRNA in the field of development and disease is highlighted. Computational and experimental approaches to identify novel miRNA, its expression and targets are also explained. The complex nature of miRNAs remains a mystery and their role in RNA interference makes it a potential target for future studies. (C) 2011 Elsevier Inc. All rights reserved.