Infrared spectroscopy provides a means to distinguish natural from synthetic emeralds in the range 2000-5000 cm^-1, as determined by a study of spectra obtained from 37 natural, 19 hydrothermal synthetic, and 38 flux synthetic emeralds from a variety of sources. The technique is nondestructive and, with Fourier transform instrumentation, extremely rapid in comparison to most laboratory methods. It is especially useful for identifying stones that contain no distinguishing inclusions. -- AATA