I will describe the Murchison Widefield Array (MWA), a new low frequency (80 - 300 MHz) interferometer that consists of 128 aperture array "tiles" with a maximum baseline of 3 km. The MWA is located in the pristine environment of remote Western Australia, one of the two sites that will host the Square Kilometre Array (SKA), and is the only low frequency Precursor for the SKA (one of three official Precursors). The science mission for the MWA includes: the search for redshifted HI signals from the Epoch of Reionisation (EoR); studies of fast and slow transients and variable objects; large-scale galactic and extragalactic continuum surveys (full Stokes); and studies of solar, heliospheric and ionospheric phenomena. Key characteristics that enable the suite of MWA science goals include its very wide field of view (~600 sq. deg. corresponding to primary beam FWHM at 150 MHz), flexible signal processing backend, and massive data archive capability. I'll describe the completion of the construction phase of the instrument, its capabilities, the science mission, results from science commissioning and the commencement of full science operations expected from July 2013. I will briefly describe the central role the MWA will play during the SKA pre-construction phase (2013 - 2016), particular to the development of the low frequency SKA.