The ASKAP Variables and Slow Transients survey gives us an unprecedented opportunity to investigate the sky at radio wavelengths for highly variable and transient sources on timescales as short as 5 seconds. ASKAP’s wide-field survey capabilities will enable the discovery and investigation of variable and transient phenomena from the local to the cosmological including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, intra-day variables, radio supernovae and the orphan afterglows of gamma-ray bursts. VAST will probe unexplored regions of phase space where new classes of transient sources may be detected.