We exploited, optimized, and developed various microscopy techniques for analyzing living matter at cellular and molecular levels. In particular, we developed a toolbox for single particle tracking (SPT) of membrane receptors and their ligands, suitable also for relatively fast single-pass membrane receptors; this is based on chemical tagging of recombinant proteins, TIRF microscopy, and automatized analysis of single particle trajectories. We are now extending it to simultaneous visualization and analysis of two moieties. The superresolved localization of this technique allowed analyzing functions, interactions and stoichiometry of (pro)neurotrophin receptors p75NTR and TrkA and of their ligands in living cells, with particular attention on some of their existing or used mutants. The analysis also after treatments with ligands or drugs unraveled their mode of action in the first steps of sundry signaling pathways.