MicroRNAs (miRNAs) are endogenous small RNAs of 21–22 nucleotides with a big role in gene regulation. They base-pair with the 3’UTR of a targeted mRNA and causes translation repression and/or degradation. Inevitably, they play a big role in disease pathology. We study the fundamental biology of cell intrinsic miRNA and extracellular miRNA that are found in cell free body fluids and apply our findings disease diagnosis and treatment.