The missions planned for the 1990’s will greatly expand our knowledge of close binary systems and the physical phenomena that can be studied in a member of a close binary, from stellar active regions to the highest density black hole candidates known. These sysems and the phenomena are reviewed with reference to major outstanding questions, our expected capability to answer them, and the expansion of capability that would be necessary. A ‘‘super’’ XMM or LAMAR experiment with larger area, but similar moderate energy resolution and moderate spatial resolution, could detect 0.1 millisecond bursts from Cyg X‐1 and 1 millisecond bursts in quiescent black hole candidates, measure Doppler and gravitational energy shifts in the iron line features for black holes and neutron stars. It would also identify these objects in galaxies a few Mpc away and open the way for evolution studies. A somewhat less ambitious goal would be high energy resolution of about the area of LAMAR to make full use of the information in the emission lines in both normal and compact binaries. Much less ambitious with respect to the hardware, but very useful to the astrophysics of these systems would be a melding of a small x‐ray spectroscopy experiment of about the area of BBXRT of AXAF with a UV package like that of IUE.