Impurity is not a much-liked word by pharmaceutical and industry people, because they are concerned about quality. Here we discuss various impurities that might be present in API formulations. To fulfill our purpose we have compiled a variety of regulatory authorities’ guidelines (i.e., ICH, WHO, and pharmacopoeias), which serve in endlessly regulating the impurities by various means. As the impurity present in a drug can affect its quality and thus its efficiency, it is therefore crucial to know about impurities. The current article reveals the different terms, regulatory control, and basic techniques (e.g., HPLC, LC-MS, TLC) that will help novices to understand, identify, and quantitatively estimate impurities and that have the advantage of profiling. This article primarily focuses on identification and control of various impurities (i.e., organic, inorganic, and genotoxic). For any of the substances, quality is the prime objective. Because impurities can alter quality, understanding the various impurities will help in producing quality products.