This book describes the reactive extraction of carboxylic acids (propionic, acetic, formic and butyric acids) from aqueous solution using organophosphorous (tri-n-butyl phophate) and amine (tri-n-octyl amine) based extractant dissolved in different active and inactive diluents. Equilibrium experiments are carried out to investigate the effect of acid and extractant concentration, diluent on the extraction efficiency. The performance of the extraction process is analyzed by calculating distribution coefficient, degree of extraction and loading ratio. Also, theoretical studies are performed to estimate the equilibrium parameters.