This chapter provides a brief review of the concepts of acid-base chemistry with its applications on drug molecules. It also highlights the significance of salt formations in pharmaceutical products. After studying this chapter, students will be able to: • Comprehend the Arrhenius, Brønstead-Lowry, and Lewis concepts of acids and bases. • Comprehend the ionization, factors controlling ionization, and the acids-base strengths. • Identify the acids and bases occurring in drug molecules and their significance. • Apply the concept of acid-conjugate base and base-conjugate acid in pharmacy. • Apply Henderson-Hasselbalch equation and in pharmacy and drug action and bioavailability. • Interpret pH partition theory and its significance in drug pharmacokinetics. • Illustrate the purpose of salt formation with drug molecules and the acidity or basicity of the salts.