  Astrometry as a technique has so far proved of limited utility when employed
as either a follow-up tool or to independently search for planetary mass
companions orbiting nearby stars. However, this is bound to change during the
next decade. In this review, I start by summarizing past and present efforts to
detect planets via milli-arcsecond astrometry. Next, I provide an overview of
the variety of technical, statistical, and astrophysical challenges that must
be met by future ground-based and space-borne efforts in order to achieve the
required degree of astrometric measurement precision. Then, I discuss the
planet-finding capabilities of future astrometric observatories aiming at
micro-arcsecond precision, with a particular focus on their ability to fully
describe multiple-component systems. I conclude by putting astrometry in
context, illustrating its potential for important contributions to planetary
science, as a complement to other indirect and direct methods for the detection
and characterization of planetary systems.
