MicroRNAs (miRNAs) are a class of ∼22nt non-coding RNAs that regulate the translational potential and stability of mRNAs. Though constituting only 1-4% of human genes, miRNAs are predicted to regulate more than 60% of all mRNAs. The action of miRNAs is mediated through their associations with Argonaute proteins and mRNA targets. Previous studies indicated that though the majority of Argonaute proteins is diffusely distributed in the cytoplasm, a small fraction is consistently observed to be concentrated in a cytoplasmic compartment called GW/P-bodies. In this chapter, we will provide a quantitative and dynamic view of the subcellular localization of miRNA function, followed by a discussion on the possible roles of PBs in miRNA silencing.