  Follow the big stars! I review the theory of detection and parameter
measurement of planetary systems by follow-up observations of ongoing
microlensing events. Two parameters can generically be measured from the event
itself: the planet/star mass ratio, $q$, and the planet/star separation in
units of the Einstein ring. I emphasize the advantages of monitoring events
with giant-star sources which are brighter (thus easier to monitor) and bigger
(thus offering the prospect of measuring an additional parameter from
finite-source effects: the proper motion $\mu$). There is potentially a strong
degeneracy between $q$ and $\mu$. I present a simple analytic representation of
this degeneracy. I then describe how it can be broken using accurate
single-band photometry from observatories around the world, or optical/infrared
photometry from a single site, or preferably both. Both types of observations
are underway or will be soon. Monitoring of giant-star events seen toward the
bulge is also the best way to determine the content and structure of the inner
Galaxy.
