Microscopy based on the interferometric detection of light scattered from nanoparticles (iSCAT) was introduced in our laboratory more than a decade ago. In this work, we present various capabilities of iSCAT for biological studies by discussing a selection of our recent results. In particular, we show tracking of lipid molecules in supported lipid bilayers (SLBs), tracking of gold nanoparticles with diameters as small as 5 nm and at frame rates close to 1 MHz, 3D tracking of Tat peptide-coated nanoparticles on giant unilamellar vesicles (GUVs), imaging the formation of lipid bilayers, sensing single unlabelled proteins and tracking their motion under electric fields, as well as challenges of studying live cell membranes. These studies set the ground for future quantitative research on dynamic biophysical processes at the nanometer scale.