The chapter "Hydrogen Bonding in Solids. Correlation of Spectroscopic and Crystallographic Data" by A. Novak from the Laboratoire de Chimie Physique, C.N.R.S., discusses the relationship between spectroscopic data and crystallographic data in the context of hydrogen bonding. The introduction highlights the modification of the potential energy function of an AH group when it forms a hydrogen bond, leading to shifts in vibrational frequencies and changes in bond distances. The chapter classifies hydrogen bonds based on their strength, using both the AH stretching frequency and bond distances as criteria. It also explores the correlation between these frequencies and distances, including the effects of isotopic substitution on the proton position. The text further examines the geometrical changes detected by neutron and X-ray diffraction methods and concludes with a discussion on the distinction between weak and strong hydrogen bonds.The chapter "Hydrogen Bonding in Solids. Correlation of Spectroscopic and Crystallographic Data" by A. Novak from the Laboratoire de Chimie Physique, C.N.R.S., discusses the relationship between spectroscopic data and crystallographic data in the context of hydrogen bonding. The introduction highlights the modification of the potential energy function of an AH group when it forms a hydrogen bond, leading to shifts in vibrational frequencies and changes in bond distances. The chapter classifies hydrogen bonds based on their strength, using both the AH stretching frequency and bond distances as criteria. It also explores the correlation between these frequencies and distances, including the effects of isotopic substitution on the proton position. The text further examines the geometrical changes detected by neutron and X-ray diffraction methods and concludes with a discussion on the distinction between weak and strong hydrogen bonds.