MicroRNAs (miRNA) are small, non-coding RNA molecules that function broadly as negative regulators of gene expression to control a wide range of cellular processes. Thousands of miRNAs have been identified in humans, but only a small fraction of them have demonstrated functional roles. Among them, miRNAs involving human diseases, especially cancer, have attracted great interest. With the discovering of new microRNAs and the uncovering of their importance various biological functions as small regulatory elements, miRNA research is rapidly evolving. miRNA sequencing is used to discover novel miRNAs, examine the dierential expression of all miRNAs and to characterize variations with single-base resolution.