The science goals of the MWA are dominated by three key projects which drive the design, with several other applications attracting interest.

The three key projects are detection and characterization of redshifted 21cm neutral hydrogen signals from the Epoch of Reionization, a high sensitivity survey of the dynamic radio sky, and measurements of the Sun and the heliospheric plasma, including constraints on the magnetic field in coronal mass ejections (CMEs). Other science enabled by the MWA includes pulsar studies of various kinds, radio recombination line mapping, and high resolution probes of the local interstellar medium.

For the Epoch of Reionization (EOR), the MWA will have sufficient sensitivity to make a high-SNR measurement of the power spectrum of fluctuations in the 21cm line, and is also expected to detect "holes" in the 21cm emission due to local ionization caused by quasars beyond z=6.5. The primary issue is not raw point-source sensitivity, but instead field of view and control of systematics, which affects the accuracy of foreground removal. The MWA design is highly optimized for these qualities, and holds a strong advantage relative to competing projects in this high-profile research area.

Solar, Heliospheric and Ionospheric research (SHI) with the MWA employs scintillation and Faraday rotation as lambda-squared propagation effects with which to perform remote sensing over a large volume of space inside 1 AU. Measurements throughout this volume are currently scarce, yielding few constraints on heliospheric models and compromising space weather prediction capabilities. The MWA has the goal of dramatically improving the quality and quantity of measurements, crucially including constraints on magnetic field strength and direction through Faraday rotation measurements, thereby revolutionizing the field.

The MWA survey of the dynamic radio sky will have a sensitivity to transient radio events that is 6 orders of magnitude better than that of any previous experiment, due to a combination of large collecting area, enormous field of view, and long observing times. Several classes of transient source are candidates for detection and study, and there is good potential for serendipity.

Other than the main science goals, additional opportunities exist for scientific results in topics such as the study of pulsars, recombination lines and the interstellar medium.