Scattering-type scanning near-field optical microscopy (s-SNOM) brings the power of infrared imaging and spectroscopy to the nanometer scale. The demonstrated spatial resolution of about 10 - 20 nm opens a new era for modern applications in analytical chemistry, materials and bio sciences. However, s-SNOM progress beyond qualitative analysis of sample surfaces has so far been impeded by the complicated nature of sample probing mechanism. The latter involves near-field interaction between a sharp illuminated probe and a sample beneath it, which hinders the recovery of quantitative information (such as dielectric permittivity) and data interpretation for three-dimensional sample. My talk will provide an overview of s-SNOM fundamentals and present recent achievements in broadband infrared nanospectroscopy (nano-FTIR) of polymers and proteins. I will further show the traditionally unthinkable: the determination of complex-valued local permittivity and thickness of simple 3D structures from near-field measurements. Thus I will demonstrate the ability of near-field microscopy to extract the same information about sample properties as returned by advanced far-field techniques such as ellipsometry, but with unprecedented nanoscale spatial resolution. Our accomplishment is based on the novel semi analytic model of tip-sample interaction and complete utilization of data outputted by typical s-SNOM instruments. Our work enables quantitative nanoscale-resolved optical studies of thin films, coatings, and functionalization layers, as well as the structural analysis of multiphase materials. It represents a major step toward near-field nanotomography.