  We present the spectral atlas of sources observed in low resolution with the
Infrared Spectrograph on board the Spitzer Space Telescope. More than 11,000
distinct sources were extracted using a dedicated algorithm based on the SMART
software with an optimal extraction (AdOpt package). These correspond to all
13,000 low resolution observations of fixed objects (both single source and
cluster observations). The pipeline includes image cleaning, individual
exposure combination, and background subtraction. A particular attention is
given to bad pixel and outlier rejection at the image and spectra levels. Most
sources are spatially unresolved so that optimal extraction reaches the highest
possible signal-to-noise ratio. For all sources, an alternative extraction is
also provided that accounts for all of the source flux within the aperture.
CASSIS provides publishable quality spectra through an online database together
with several important diagnostics, such as the source spatial extent and a
quantitative measure of detection level. Ancillary data such as available
spectroscopic redshifts are also provided. The database interface will
eventually provide various ways to interact with the spectra, such as
on-the-fly measurements of spectral features or comparisons among spectra.

Instrumentation and Methods for Astrophysics;Cosmology and Nongalactic Astrophysics;Astrophysics of Galaxies;Solar and Stellar Astrophysics