Searches for binary stars in globular clusters.

Binary stars have been identified in globular clusters using X-ray emission, eclipses, radial velocity variations, and their position in the color-magnitude diagram (CMD). The last few years have seen rapid progress in identifying eclipsing variables using large sets of CCD images. The deep CMDs of the centers of clusters produced from HST images, are poised to revolutionize the identification of "binary sequences" in the CMD. Surveys for radial velocity variables are being extended to fainter stars and longer time baselines. Each search technique has its strengths and weaknesses. Surveys for eclipsing systems are currently a relatively unique window into the number of short-period binaries, binary sequences are sensitive to systems with a wide range of periods, and radial velocity surveys can, eventually, determine the distributions of orbital properties. The present paper reviews what is currently known of the binary star poulations in globular clusters and outlines prospects for future research in this field.