How do events taking place at the molecular level translate to biologically significant phenomena? We develop single molecule and nanoscopic optical imaging techniques to understand this basic question. Biology, as we know it, is the culmination of many singular events like the generation of 'a' mRNA from 'a' DNA by 'a' RNA polymerase. Yet, our understanding of most biological processes comes from ensemble studies of the molecules carried out in a tube or using reporters in cells and organisms. Mechanistic understanding of biological phenomena is complicated by - the heterogeneity among biomolecules (due to modifications or conformational dynamics) - the transient nature of interactions (activating action of molecule maybe limited to a fraction of its lifetime) and - the limits on detection of small number of molecules. The goal of our research efforts is to bypass these issues by probing the behaviour of single molecules directly.