  The evidence for spectral features in gamma-ray bursts is summarized. As a
guide for evaluating the evidence, the properties of gamma-ray detectors and
the methods of analyzing gamma-ray spectra are reviewed. In the 1980's,
observations indicated that absorption features below 100 keV were present in a
large fraction of bright gamma-ray bursts. There were also reports of emission
features around 400 keV. During the 1990's the situation has become much less
clear. A small fraction of bursts observed with BATSE have statistically
significant low-energy features, but the reality of the features is suspect
because in several cases the data of the BATSE detectors appear to be
inconsistent. Furthermore, most of the possible features appear in emission
rather than the expected absorption. Analysis of data from other instruments
has either not been finalized or has not detected lines.
