MicroRNAs (miRNA) have become a crucial player in the realm of life sciences due to their significance. MiRNAs, tiny non-coding RNAs inherent to an organism, serve as crucial regulators of gene expression at the post-transcriptional level. It has been demonstrated that these minute RNAs have the capability to control processes such as cell growth, differentiation, and programmed cell death known as apoptosis. Through their interaction with complementary sequences in messenger RNAs (mRNAs), miRNAs modulate mRNA expression, consequently impacting the expression of endogenous genes via mechanisms such as mRNA cleavage or translational inhibition. A sole miRNA possesses the ability to modulate the regulation of numerous distinct mRNAs, suggesting its potential influence on a significant portion of the mRNA repertoire encoded within the human genome. In this regard, our chapter explores the potential applications of miRNAs in the realms of development and diseases. Furthermore, it delves into the computational and experimental methodologies utilized to discover new miRNAs, elucidate their expression patterns, and identify their targets. The intricate nature of miRNAs poses a challenge as their exact functions and mechanisms remain shrouded in mystery, particularly given their involvement in RNA interference, which makes them an attractive subject for prospective investigations.