One of the great astronomy stories of the 1990's was the discovery of
microlensing events. The scientific messages encoded in those events are 
only partially understood. Wide-field surveys about to begin should lead to
the discovery of thousands of events per year. We will discuss the
challenges both observers and theorists must face if we are to use those
events to optimize the discovery of planets (nearby planets as well as those 
many kpc away), and derive a reliable estimate of the contribution of MACHOs 
to dark matter.