Stability testing is a crucial part of the pharmaceutical development process that ensures the safety, efficacy, and quality of a drug product throughout its shelf life. This testing involves subjecting the product to various environmental condition, such as temperature, humidity, and light, to evaluate how these factors affect its physical, chemical, and microbiological properties. Stability studies help determine the appropriate storage conditions, expiration date, and packaging requirements for a pharmaceutical product. The tests are typically conducted under accelerated, intermediate, and long-term conditions, with samples analyzed at predefined intervals. The data obtained from stability testing also play a critical role in a regulatory approval process, providing evidence that the product remains within specifications throughout its intended shelf life. Furthermore, stability testing is an ongoing process that continuous post-market to monitor any potential changes or degradation that may occur during distribution or consumer us. This paper reviews the principles, methodologies, and importance of stability testing, highlighting its role in ensuring the reliability of pharmaceutical products in the market.