Our understanding of stellar evolution depends on knowing beta-decay rates and reaction crosssections for a wide range of nuclear capture reactions. Direct laboratory measurements ofimportant stellar reaction rates are hindered by low cross sections and, in some cases, the needfor radioactive targets. Indirect techniques have been developed to determine reaction rates forsystems that are particularly difficult to measure in a direct experiment. One of the indirecttechniques involves measurements of Asymptotic Normalization Coefficients (ANCs) whichdetermine the direct-capture contribution to a capture reaction. Also ANCs can be used tounderstand the role of subthreshold states in stellar capture. This essay gives an introduction toANCs and describes how they are used in nuclear astrophysics. Examples are given ofmeasurements which have been carried out with both stable and radioactive beams.