The monograph contains discussion of experimental and theoretical studies of intermolecular interactions and aggregation of molecules in the liquid state. Particular attention is paid to the intermolecular hydrogen bond and aggregation of molecules in liquids and solutions through this interaction. Problems of the formation of molecular aggregates were solved using Raman spectroscopy and quantum-chemical calculations based on the Gaussian-98 software. The material is the result of research activities by the staff of the Problem Laboratory named after Acad. A.K. Atahodzhaev at the Chair of Optics and Spectroscopy of Samarkand State University in the last 20 years. The material will contribute to the development of the theory of liquid state, the problem, which is not solved completely up to date. Progress in the theory of liquids and solutions will contribute to the development of several areas of physics, physical chemistry, biology and nanotechnology, as well as targeted use of liquid media and solutions for the needs of production. The monograph is intended for a wide range of scientists, researchers, graduate students, masters and bachelor students of senior courses of university.