  In this paper, we describe the wide-field spectroscopic survey telescope
(WST) project. WST is a 12-metre wide-field spectroscopic survey telescope with
simultaneous operation of a large field-of-view (3 sq. degree), high-multiplex
(20,000) multi-object spectrograph (MOS), with both a low and high-resolution
modes, and a giant 3x3 arcmin2 integral field spectrograph (IFS). In scientific
capability, these specifications place WST far ahead of existing and planned
facilities. In only 5 years of operation, the MOS would target 250 million
galaxies and 25 million stars at low spectral resolution, plus 2 million stars
at high resolution. Without need for pre-imaged targets, the IFS would deliver
4 billion spectra offering many serendipitous discoveries. Given the current
investment in deep imaging surveys and noting the diagnostic power of
spectroscopy, WST will fill a crucial gap in astronomical capability and work
in synergy with future ground and space-based facilities. We show how it can
address outstanding scientific questions in the areas of cosmology; galaxy
assembly, evolution, and enrichment, including our own Milky Way; the origin of
stars and planets; and time domain and multi-messenger astrophysics. WST's
uniquely rich dataset may yield unforeseen discoveries in many of these areas.
The telescope and instruments are designed as an integrated system and will
mostly use existing technology, with the aim to minimise the carbon footprint
and environmental impact. We will propose WST as the next European Southern
Observatory (ESO) project after completion of the 39-metre ELT.
