This review discusses solubilizing excipients used in oral and injectable formulations. Common solubilizing excipients include water-soluble organic solvents, non-ionic surfactants, water-insoluble lipids, organic liquids/semi-solids, cyclodextrins, and phospholipids. Techniques for solubilizing water-insoluble drugs include pH adjustment, cosolvents, complexation, microemulsions, self-emulsifying drug delivery systems, micelles, liposomes, and emulsions. The key aspects of successful solution formulations are solubility and stability. The solvent system must solubilize the drug at the desired concentration and provide a stable environment. Stability is defined as less than 5–10% degradation over 2 years under storage conditions. Solubility is influenced by the free energy of the solid and the solution. Increasing solubility can be achieved by altering the solid state or by reducing the chemical potential of the molecule in solution. Excipients that solubilize via bulk solution properties reduce the chemical potential, requiring higher solution concentration for solubility. Excipients that solubilize via specific interactions, such as complexation, lower the chemical potential through noncovalent interactions. pH adjustment can increase water solubility by ionizing the molecule. For weak acids, solubility increases with pH above the pKa, while for weak bases, solubility increases with pH below the pKa. Cosolvents are used to solubilize water-insoluble drugs, with solubility increasing logarithmically with the fraction of organic solvent. Complexation can significantly enhance solubility, with cyclodextrins achieving solubility enhancements up to 10⁴ to 10⁵. Emulsions can solubilize water-insoluble molecules by partitioning them into the oil phase. Oral formulations include solutions, syrups, elixirs, and solutions in capsules. These formulations are used to enhance bioavailability, allow dose modification, and accommodate patients who cannot swallow tablets or capsules.This review discusses solubilizing excipients used in oral and injectable formulations. Common solubilizing excipients include water-soluble organic solvents, non-ionic surfactants, water-insoluble lipids, organic liquids/semi-solids, cyclodextrins, and phospholipids. Techniques for solubilizing water-insoluble drugs include pH adjustment, cosolvents, complexation, microemulsions, self-emulsifying drug delivery systems, micelles, liposomes, and emulsions. The key aspects of successful solution formulations are solubility and stability. The solvent system must solubilize the drug at the desired concentration and provide a stable environment. Stability is defined as less than 5–10% degradation over 2 years under storage conditions. Solubility is influenced by the free energy of the solid and the solution. Increasing solubility can be achieved by altering the solid state or by reducing the chemical potential of the molecule in solution. Excipients that solubilize via bulk solution properties reduce the chemical potential, requiring higher solution concentration for solubility. Excipients that solubilize via specific interactions, such as complexation, lower the chemical potential through noncovalent interactions. pH adjustment can increase water solubility by ionizing the molecule. For weak acids, solubility increases with pH above the pKa, while for weak bases, solubility increases with pH below the pKa. Cosolvents are used to solubilize water-insoluble drugs, with solubility increasing logarithmically with the fraction of organic solvent. Complexation can significantly enhance solubility, with cyclodextrins achieving solubility enhancements up to 10⁴ to 10⁵. Emulsions can solubilize water-insoluble molecules by partitioning them into the oil phase. Oral formulations include solutions, syrups, elixirs, and solutions in capsules. These formulations are used to enhance bioavailability, allow dose modification, and accommodate patients who cannot swallow tablets or capsules.