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GC separates analytes through their different interactions with a stationary phase as a carrier gas moves them through a column. More volatile or less strongly interacting compounds generally elute sooner. The method is suited to compounds that can be vaporized and withstand heat; derivatization may help with some polar compounds. Carrier gas, flow rate, column type, temperature programming, injector, and detector are important choices. For pharmaceutical applications, GC can support residual-solvent testing, impurity profiling, chiral analysis, stability studies, and analysis of volatile compounds. Understanding quantitation, performance measures, and validation helps place GC results in an analytical context, while its limitations—such as the need for volatile, thermally stable analytes—inform whether it is suitable for a given sample.