  The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new
time domain survey employing a dedicated camera on the Palomar 48-inch Schmidt
telescope with a 47 deg$^2$ field of view and 8 second readout time. It is well
positioned in the development of time domain astronomy, offering operations at
10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a
single 1-m class survey telescope. The public surveys will cover the observable
northern sky every three nights in g and r filters and the visible Galactic
plane every night in g and r. Alerts generated by these surveys are sent in
real time to brokers. A consortium of universities which provided funding
("partnership") are undertaking several boutique surveys. The combination of
these surveys producing one million alerts per night allows for exploration of
transient and variable astrophysical phenomena brighter than r $\sim$ 20.5 on
timescales of minutes to years. We describe the primary science objectives
driving ZTF including the physics of supernovae and relativistic explosions,
multi-messenger astrophysics, supernova cosmology, active galactic nuclei and
tidal disruption events, stellar variability, and Solar System objects.
