In this talk, I will go over some synopsis of single molecule technique and usage followed by the main topic of RNP granule assembly. Ribonucleotprotein (RNP) granules are membraneless cellular compartments used for RNA storage, degradation and localization. They form liquid like droplets in cells but such property is converted to fibril or amyloid-like state in neurodegenerative diseases such as ALS and FTD which are hallmarked by pathogenic aggregation of FUS, TDP-43 and other hnRNPs. Recent studies reported on the spontaneous formation of liquid like droplets by these proteins promoted by conditions such as low salt and high protein concentration, but the molecular mechanism that gives rise to granule assembly and dynamic state of granule remains elusive. In order to find a treatment for these debilitating diseases, we need to decipher exactly how individual protein molecule interacts with RNA/protein and how this process is altered in mutants. We are employing a combination of single molecule fluorescence, biochemical, biophysical tools to dissect molecular underpinnings of granule assembly and dynamics.