In 1912, Albert Einstein realized that a distant star can exhibit a transient brightening caused by the bending of light due to the gravitational field of an intervening foreground star. However, because of the rarity of sufficiently close angular alignments, it required several decades of advances in technology until the observation of such gravitational microlensing events turned into reality. Planets around the lens star can reveal their existence with finite probability by causing blips or dips to microlensing light curves that are otherwise symmetric around a peak. Such planetary signals last between hours and weeks depending on the mass of the planet as well as the angular size of the observed source star and its proper motion with respect to the foreground ‘lens’ star. Due to a resonance effect between the deflections caused by the lens star and its planets, the latter are more easily detected if their angular separation falls into the ‘lensing zone’.