  We describe the development and implementation of the SEGUE (Sloan Extension
for Galactic Exploration and Understanding) Stellar Parameter Pipeline (SSPP).
The SSPP derives, using multiple techniques, radial velocities and the
fundamental stellar atmospheric parameters (effective temperature, surface
gravity, and metallicity) for AFGK-type stars, based on medium-resolution
spectroscopy and $ugriz$ photometry obtained during the course of the original
Sloan Digital Sky Survey (SDSS-I) and its Galactic extension (SDSS-II/SEGUE).
The SSPP also provides spectral classification for a much wider range of stars,
including stars with temperatures outside of the window where atmospheric
parameters can be estimated with the current approaches. This is Paper I in a
series of papers on the SSPP; it provides an overview of the SSPP, and initial
tests of its performance using multiple data sets. Random and systematic errors
are critically examined for the current version of the SSPP, which has been
used for the sixth public data release of the SDSS (DR-6).
