Weak chemical interactions, i.e., hydrogen and halogen bonds, underlie the formation of molecular crystals and control their structure. This book provides a description of the properties and characteristics of these interactions, as well as conclusions about their nature, made from measurements of the vibrational (Raman) spectra of a large number of compounds in the temperature range 5 K – 300 K. The diagnostic parameters of hydrogen bonds, i.e., vibration frequency, Raman intensity, band half-width and degree of anharmonicity, are described in detail, for the entire range of bonds, from weak to ultrashort, intra- and intermolecular. The results of the study of vibrational spectra of halogen-halogen bonds are also presented, which allow us to draw a certain conclusion about its nature.The book will appeal to students and scientists whose interests lie in the field of research of chemical compounds, and biological and pharmaceutics systems.