Gravitational microlensing: a method for detecting halo dark matter

It has been shown by Paczy\'nski that gravitational microlensing is potentially a useful method for detecting the dark constituents of the halo of our galaxy, if their mass lies in the approximate domain $10^{-6} < M/M_{\odot} < 10^{-1}$. Microlensing observations now under way monito several millions of stars in the Large Magellanic Cloud and in the Galactic Bulge. Here I discuss the main features of the microlensing events: in particular their rates and probability, taking also into account a possible flattened shaper for the halo.