Drug formulations contain active pharmaceutical ingredients (APIs) and excipients. APIs present in the formulations contain some undesired impurity, which affects purity of the APIs. Therefore, with along % purity, impurity profiling is also needed to be carried out of all the APIs. Impurity profiling describes the account or description of maximum possible types of identified or unidentified impurities present in any APIs. These impurities can be API related impurities, process related impurities or stability related impurities. API related impurities include stereochemistry, crystallization, and functional group of APIs. Process related impurities include chemicals, reagents, catalysts, residual solvents, synthetic intermediate products, by product, degradation products, method conditions related impurities, and formulation related impurities. Stability related impurities include degradation or transformation of APIs, mutual interactions among APIs, excipients present in drug product. Presence of these unwanted impurities may influence bioavailability, safety and efficacy of APIs. Various regulatory authorities such as ICH, USFDA etc., have specified various limits for impurities in APIs. Along with the routine use of authentic markers and analytical techniques, isolation and characterization of impurities are required for acquiring the data that establishes biological safety and efficacy. In the recent trends impurity profiling emerges out as a mandatory requirement for a new drug application. The present review describes probable sources of impurities, need for impurity profiling and detailed techniques of characterization and quantitation of impurities. Thus, this review is an attempt to understand concept of impurity profiling and its various aspects.