Modern telescopes and equipments have permitted excellent ground-based observations of Mercury, despite its proximity to the Sun. This is one of the main reasons why it has been observed using different techniques from high-resolution spectroscopy to high-resolution imaging from visible to infrared up to radio wavelengths. Because there is no obscuration from a thick atmosphere, the surface and exosphere have been imaged and the surface studied by infrared spectroscopy. This manuscript describes the techniques used to obtain information and new data of Mercury giving an overview of advantages and difficulties, and describes important scientific discoveries made with specific telescopic instrumentation.