WEAVE is the next-generation wide-field survey facility for the William 
Herschel Telescope (WHT). WEAVE will provide the instrument required for 
full scientific exploitation of the Gaia, LOFAR, and APERTIF surveys in 
the Northern Hemisphere. WEAVE is a multi-object and 
multi-integral-field-unit (IFU) facility utilizing a large, 
new 2-degree-diameter prime focus corrector at the WHT with a 
pick-and-place fibre positioner system hosting nearly 1000 multi-object 
fibres or 20 mini-IFUs for each observation, or a single wide-field IFU. 
The fibres are fed into a dual-beam spectrograph located in the GHRIL 
enclosure on the WHT's Nasmyth platform. The spectrograph records nearly 
1000 spectra simultaneously at a resolution of R~5000 over an instantenous 
wavelength range of 366-959 nm or at a resolution of R~20000 over two 
more-limited wavelength ranges. WEAVE will be on sky in early 2019 to 
provide complete phase-space coordinates of more than 5 million stars in 
the northern sky selected with ESO’s Gaia satellite, distances and 
properties of galaxies selected from the low-frequency radio-wave surveys 
being conducted with LOFAR, “three-dimensional" spectroscopy of galaxies 
selected from surveys using the new Apertif focal plane array at the 
Westerbork Radio Synthesis Telescope, deep surveys of galaxy clusters and 
moderate-redshift galaxies, and the scale of the Universe at z~2-4 from 
quasar absorption lines. In this talk I will discuss WEAVE's basic science 
drivers, why we made the choices we did, and the current status of the 
instrument development and science preparation.