Stability studies are a cornerstone of pharmaceutical quality assurance, ensuring that drug products retain their identity, strength, purity, and performance throughout their shelf life. The main objective of stability testing is to provide evidence on how environmental factors such as temperature, humidity, and light affect the quality of a drug product. This review outlines the principles and types of stability studies, the influence of various factors on drug stability, and the regulatory guidelines governing stability testing. Emphasis is placed on ICH Q1A (R2) guidelines, real-time and accelerated studies, and their role in establishing expiration dates and storage conditions. The importance of stability data in maintaining consistent product quality, ensuring patient safety, and meeting regulatory expectations is also discussed.