Microwave dielectric spectroscopy (MDS) is an online, compact, non-destructive/invasive, low power analytical methodology based upon the rotation of molecules and their functional groups in the presence of an electromagnetic field in the frequency range of 0.3–300 GHz which may then be used to differentiate materials of different composition. Recent technological developments have increased the availability of the equipment needed to investigate the application of MDS within the food industry. This article gives an overview of the fundamentals of the technology and a review of potential applications in the food industry. Challenges and the future potential of this technology are also considered.