Among the different methods to characterize the structures of fibril polymorphs, vibrational spectroscopy techniques such as Raman scattering and infrared (IR) absorbance offer several advantages. Compared to gold-standard methods such as solid-state NMR (ssNMR) and cryo-electron microscopy (cryo-EM), data acquisition using vibrational methods is relatively fast and robust. Additionally, fibrils can be studied with relatively little preparation and small quantities (< 1 mg) in a variety of sample states, including fibrils in solution, gels, films, and directly in biological tissues. Most vibrational spectroscopy structural studies on fib-rils focus on the fingerprint region (∼ 1000 -1700 cm -1 ), which contains Raman and IR bands that derive from vibrations localized to chemical bonds and functional groups of the peptide backbone and amino acid side chains. The frequencies and intensities of these bands provide insights into the (sub)molecular structures and interactions within fibrils. For instance, the Amide I mode (mainly C--O stretching of backbone amides) can be used to distinguish between parallel and antiparallel β-sheet structures and quantitatively assess the strength of hydrogen bonding interactions between strands. The Amide III mode, which derives from amide CN stretching and NH bending, can be used to measure the distribution of Ramachandran ψ-angles adopted by peptide bonds in fibrils. Thus, these and other vibrational bands enable the facile differentiation of structural features and interactions between different fibril polymorphs.