Nanogranular metals combine the unique properties of individual and collective properties of coupled nanocrystals opening a new route for potential novel electronic, optical, and optoelectronic applications. The ease of adjusting electronic properties of granular metals makes them most suitable for fundamental studies of mesoscopic physics. In this talk, I will firstly review the theoretical and experimental advances in three areas of this field. These include: 1) the influence of many-body Coulomb interaction on the transport properties of granular metals; 2) multi-percolation transitions phenomenon in nanogranular systems; 3) the critical behaviors in granular superconductors near the superconductor-insulator transition. I will also discuss our recent studies in each area.