RNA interference is an exciting field of functional genomics that can silence viral genes.  This property of interfering RNA can be used to combat viral diseases of plants as well as animals and humans.  It is a short sequence of nucleic acid that can bind to the mRNA of the gene and interferes the process of its expression.  It is diverse in occurrence as well as in applications.  It occurs from nematodes to fungi and can cause gene silencing in plants, animals and human beings.  Small interfering RNAs are used to silence plant viral genes and in production of therapeutic drugs against Hepatitis or Immuno-deficiency viruses in human.  In this review, we will discuss the history, mechanism and applications of RNA interference in plant, animal and human research.