Proteins consist of a unique sequence of amino acids that are connected by peptide bonds and these repeating units of amino acids (-CO-CR-NH-) possess polar characteristics. In addition, these amino acid side chains can be neutral, polar, or charged, further contributing to their polarizability. Due to their polarizability, they are sensitive to dielectric techniques and present specific dielectric constant in defined conditions. The protein formulation conditions such as plasticizer additives, pH, moisture content, and temperature affect the dielectric properties of the protein, including electronic and atomic polarization, dipolar reorientation, and space-charge interfacial polarization. As such, dielectric spectroscopy (DES) was widely used as a direct approach for relaxation and dynamic and antiplasticization measurement for glassy and small molecules. DES is commonly used to probe protein motions across a wide frequency from 10 -6 to 10 10 Hz and temperature ranges. In many cases, the dynamics of proteins are studied in aqueous solutions or different hydration levels or solvent systems. The broad frequency range was used to probe the fast coupled proteinhydration water relaxation and slow relaxation of large-scale domain-like motions of proteins such as lysozyme and myoglobin. More specifically, megahertz (MHz) to terahertz (THz) dielectric spectroscopy probes dynamic processes between 10 -6 and 10 -12 s and bulk water relaxation near 20 GHz and protein tumbling near 1-10 MHz can be identified simultaneously. The reorientation motion of protein such as myoglobin as a local β-relaxation was observed in the sub-MHz frequencies. In addition, the protein hydration as preferential exclusion and protein-water interaction induced protein dynamic changes were studied. For example, lysozyme is found to surrounded by a tightly bound layer of ~165 water molecules in terms of picosecond dynamic through the dielectric response analysis over the range of 65 to 700 GHz. Furthermore, DES was utilized to explore different orientational polarization mechanisms including relaxation, such as the dynamics of loosely bound, tightly bound, and bulk water and investigate the collective vibration motions of protein and protein-water interaction. 138 However, these techniques pose challenges in lyophilized solids due to the impact of their moisture water content and their porous structure. In one of the very few demonstrations of its use in solid protein formulation, mechanistic understanding of sugar-induced protein stabilization via DES was investigated through protein embedded in a sugars and water system which comprehensive relaxation of sugar, water, solvent, and protein was studied. Large-scale conformational myoglobin motion induced slower protein relaxation was observed due to the relaxation of trehalose below Tg, which was associated with intramolecular rotations of the monosaccharide rings in trehalose.