<p>With the growing severity of environmental issues, the pollution and toxicity associated with conventional chemical processes have drawn increasing concern. Since most chemical reactions rely on solvents, the development of non-toxic, environmentally benign, and recyclable green solvents is essential for advancing sustainable chemistry and engineering. Among these, deep eutectic solvents (DESs) have emerged as a promising class of alternative solvents characterized by low volatility, tunability, cost-effectiveness, and straightforward preparation. As a result, DESs are increasingly being employed as replacements for traditional organic solvents, garnering significant attention in applications such as the extraction of natural products and chromatographic separations. This review comprehensively examines recent advances in DESs research, delving into their fundamental characteristics—including definition, classification, and preparation methods—and provides a detailed overview of their applications in pharmaceutical chemistry. The article also discusses current challenges and future prospects in the field. It is anticipated that this work will contribute to the continued development and rational design of DESs for sustainable chemical processes.</p>