Ultrasonic's has been an important tool in determining the nature of molecular interactions in the solutions of all types of liquids. Standard techniques have been employed in measuring ultrasonic velocity, density and viscosity at different temperatures. The present study is divided into three major categories-1) Binary mixtures containing DMSO as common component, 2) Solutions of insecticides/pesticides in various types of organic solvents and 3) The effect of electrolytes in the aqueous solutions of t-butanol. Also theoretically evaluated velocities have been compared with the experimental ones. Excess thermodynamic parameters have been computed and their variation with concentration is discussed in the light of molecular interactions like dipole-dipole, charge transfer, dispersive forces etc. In the solutions of insecticides mostly solute-solvent interactions are suggested. From the apparent molar volumes, apparent molar compressibilities and viscosity coefficients A and B, solute-solvent interactions have been studied and a comparison is made among the electrolytes. This book is intended for the experts of Ultrasonic field as well as post-Graduate students and researchers.