What Is SIMBAD, and What Is It Not?

The purpose of the SIMBAD database is to provide the bibliography and some fundamental data on astronomical objects of interest which have been studied in scientific articles. It includes objects of any nature, stars - galaxies - interstellar medium - transient events - etc. SIMBAD is a meta-compilation built from what is published in the literature, and from our expertise on cross-identifications. It is a dynamic database, updated every working day. By construction its content is heterogeneous as data come from any kind of instruments at all wavelengths with any resolution and astrometry, and different names from one publication to another. Thus SIMBAD is not a catalogue, and should not be used as a catalogue. It is not the purpose of SIMBAD to contain "everything". Especially, lists of uncharacterised sources detected in photometric surveys of any size are usually not processed in SIMBAD. But they are available at CDS in the VizieR database which contains published tables of objects, as well as most very large surveys. The idea now is to use both SIMBAD and VizieR as complementary research tools.