The Murchison Widefield Array (MWA) is a joint project between an international consortium of organisations to construct and operate a low-frequency radio array. 'Widefield' refers to its very large field of view (on the order of 30 degrees across). Operating in the frequency range 70–300 MHz, the main scientific goals of the MWA are to detect neutral atomic Hydrogen emission from the cosmological Epoch of Reionization (EoR), to study the sun, the heliosphere, the Earth's ionosphere, and radio transient phenomena, as well as map the extragalactic radio sky. It is located at the Murchison Radio-astronomy Observatory (MRO). Along with the Australian Square Kilometre Array Pathfinder (ASKAP), also at the MRO, and two radio telescopes in South Africa, the Hydrogen Epoch of Reionization Array (HERA) and MeerKAT, the MWA is one of four precursors to the international project known as the Square Kilometre Array (SKA). Development The MWA was to be situated at Mileura Station where initial testing had been conducted then moved southwest to Boolardy Station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO), north of Perth. This location offers a quiet radio environment and stable climate for observations. The MRO is also the site of CSIRO's Australian Square Kilometre Array Pathfinder (ASKAP) and one of two selected sites in Australia for the Square Kilometre Array (SKA). In addition to the geographic link, the MWA is one of four official SKA precursor telescopes – instruments that provide instrumental, scientific and operational information to help guide SKA developments, along with two sites in South Africa, HERA and MeerKAT. The MWA was initially conceived as a 512-tile instrument (512T) to be built in stages. The first stage was a 32-tile prototype (MWA-32T) which was constructed and operated with increasing capability over the period 2007–2011, testing telescope hardware and making preliminary science observations, including initial observations of EoR fields. The first phase of the telescope, the so-called "Phase I MWA" achieved full practical completion in late 2012 and completed commissioning on 20 June 2013, before moving into full operations. The Phase I MWA fully cross-correlates signals from 128 phased tiles, each of which consist of 16 crossed dipoles arranged in a 4x4 square. As part of a planned future roll out infrastructure on-site at the MRO was installed during Phase I to allow an eventual build-out to 256 tiles. The total cost of the first phase of the project was A$51