  The Planet Formation Imager (PFI, www.planetformationimager.org) is a
next-generation infrared interferometer array with the primary goal of imaging
the active phases of planet formation in nearby star forming regions. PFI will
be sensitive to warm dust emission using mid-infrared capabilities made
possible by precise fringe tracking in the near-infrared. An L/M band combiner
will be especially sensitive to thermal emission from young exoplanets (and
their disks) with a high spectral resolution mode to probe the kinematics of CO
and H2O gas. In this paper, we give an overview of the main science goals of
PFI, define a baseline PFI architecture that can achieve those goals, point at
remaining technical challenges, and suggest activities today that will help
make the Planet Formation Imager facility a reality.
