The Murchison Widefield Array is a dipole-basedaperture array synthesis telescope designed to operate in the80–300 MHz frequency range. It is capable of a wide range ofscience investigations but is initially focused on three keyscience projects: detection and characterization of threedimensionalbrightness temperature fluctuations in the 21 cmline of neutral hydrogen during the epoch of reionization (EoR)at redshifts from six to ten; solar imaging and remote sensing ofthe inner heliosphere via propagation effects on signals fromdistant background sources; and high-sensitivity exploration ofthe variable radio sky. The array design features 8192 dualpolarizationbroadband active dipoles, arranged into 512 Btiles[comprising 16 dipoles each. The tiles are quasi-randomly distributedover an aperture 1.5 km in diameter, with a smallnumber of outliers extending to 3 km. All tile–tile baselines arecorrelated in custom field-programmable gate array basedhardware, yielding a Nyquist-sampled instantaneous monochromaticuv coverage and unprecedented point spreadfunction quality. The correlated data are calibrated in realtime using novel position-dependent self-calibration algorithms.The array is located in the Murchison region of outbackWestern Australia. This region is characterized by extremelylow population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities.