This contributed volume explores the dielectric properties of biological systems, including amino acids, peptides, proteins, and water. Studying protein dynamics in aqueous solutions enables us to move beyond static snapshots of protein structures, gaining a deeper understanding of how these essential molecules function in their natural environment. Proteins are the workhorses of the cell, and their functions – from catalyzing reactions to transporting molecules and signaling – are intrinsically linked to their dynamic behavior. These movements, ranging from rapid vibrations to large-scale conformational changes, are often essential for their activity. The book covers the most essential experiments related to the dynamics of biomolecules as observed by broadband dielectric and THz spectroscopies. It also reviews the significant progress made in this field over the last twenty years. Furthermore, the dynamics of proteins are compared to those observed in other aqueous solutions of glass-forming systems. The concept of "slaving" in proteins is also explored in depth. This phenomenon refers to how certain protein motions are significantly influenced, and often dominated, by the dynamics of the surrounding solvent, especially water. Additionally, this concept is generalized to include peptides and other glass-forming systems. Furthermore, the book reports on recent advances in anisotropic THz spectroscopy and describes its advantages compared to conventional THz spectroscopy. Overall, this book provides an essential resource for researchers interested in the dynamics of biomolecules who are either using these techniques or interpreting data obtained from them.