Microwave processing of materials technology is a unique and powerful technology that can offer many advantages when compared with the conventionally already in use technology. On the other hand, lithium disilicate (LS2) glass system provides the basis for a large number of glass-ceramic products, such as cookware, radomes, ceramic composites, stovetops, and recently a new generation of dental crowns. The crystallization of lithium disilicate glass into glass-ceramic materials using variable frequency microwave (VFM) processing will be investigated in this study. The existence of the "Microwave effect" phenomena and concept in the crystallization process of LS2 as well as the possible explanations for the existence of that effect will be discussed. The molecular orbital model of microwave absorption will be used to predict the microwave absorption in LS2 glass and glass-ceramic. Finally a correlation to estimate the volume fraction of crystals in LS2 glass-ceramics materials by Fourier transform infrared spectroscopy (FTIR) will be presented.