RNA interference is the mechanism used to degrade target RNA by utilizing different mechanisms like siRNA(Short interfering RNA) and miRNA (microRNA). RNAi mechanism regulates gene expression by inhibition of translation of mRNA or by direct degradation of mRNA. This mechanism is necessary for defence against the infection by viruses, protection from transposons. By using non-coding RNA molecules like siRNA & miRNA, RNA induced silencing complex (RISC) is formed that cleaves or degrade the mRNA by attaching to the target mRNA with the help of enzymes Dicer, Drosha. Both siRNA and miRNA are distinct from where they originate. siRNA is exogenous in origin although miRNA is endogenous. siRNA is 100% complementary to the target but miRNA originates with ssRNA forming a hairpin structure which is why not 100% complementary to the target. The enzyme Dicer works in siRNA while miRNA needs one extra enzyme called Drosha along with Dicer.