Due to gravitational bending of light, a foreground ‘lens’ star passing close to the line-of-sight to an observed background star, causes an observable transient brightening, thereby creating a ‘gravitational microlensing event’. The presence of a planet orbiting the lens star can lead to an additional short blip or dip lasting from hours to weeks. A lucky coincidence with respect to the typical values of the gravitational radius of stars and distances within the Milky Way gives us the opportunity to exploit this effect for detecting planets orbiting stars (preferentially the common K-and M-dwarfs) in both the Galactic disk and bulge at separations between 1 and 10 AU. With sensitivities reaching down to planets of Earth mass and even below, gravitational microlensing allows the probing of a region of planet parameter space that is hardly accessible by other techniques.