Massive stars are born in close binaries, and in the course of their evolution, the initially more massive star will grow and begin to transfer mass and angular momentum to the gainer star. The mass donor star will be stripped of its outer envelope, and it will end up as a faint, hot subdwarf star. Here I present a search for the subdwarf stars in Be binary systems using the International Ultraviolet Explorer. Through spectroscopic analysis, I detected the subdwarf star in HR 2142 and 60 Cyg. Further analysis led to the discovery of an additional 12 Be and subdwarf candidate systems. I also investigated the EL CVn binary system, which is the prototype of class of eclipsing binaries that consist of an A- or F-type main sequence star and a low mass subdwarf. From spectroscopic analysis using both the Hubble Space Telescope Cosmic Origins Spectrograph and the Apache Point Observatory ARC Echelle Spectrograph, I computed the system's radial velocities and orbital parameters. I combined these with photometric measurements from the pt5m telescope to obtain the physical properties of the system. The detection of these subdwarf stars only represents a small fraction of their population, and follow up spectroscopy will be needed to estimate their fundamental parameters. Such information will be compared with models to trace their evolutionary history.