  The Gemini Planet Imager (GPI) has as its science instrument an infrared
integral field spectrograph/polarimeter (IFS). Integral field spectrographs are
scientificially powerful but require sophisticated data reduction systems. For
GPI to achieve its scientific goals of exoplanet and disk characterization, IFS
data must be reconstructed into high quality astrometrically and
photometrically accurate datacubes in both spectral and polarization modes, via
flexible software that is usable by the broad Gemini community. The data
reduction pipeline developed by the GPI instrument team to meet these needs is
now publicly available following GPI's commissioning.
  This paper, the first of a series, provides a broad overview of GPI data
reduction, summarizes key steps, and presents the overall software framework
and implementation. Subsequent papers describe in more detail the algorithms
necessary for calibrating GPI data. The GPI data reduction pipeline is open
source, available from planetimager.org, and will continue to be enhanced
throughout the life of the instrument. It implements an extensive suite of task
primitives that can be assembled into reduction recipes to produce calibrated
datasets ready for scientific analysis. Angular, spectral, and polarimetric
differential imaging are supported. Graphical tools automate the production and
editing of recipes, an integrated calibration database manages reference files,
and an interactive data viewer customized for high contrast imaging allows for
exploration and manipulation of data.
