Binaries as Astrophysical Laboratories: Open Questions
  Binary systems have long been recognized as the source of powerful astrophysical diagnostics. Among the many applications of binary stars, they have been used as probes of stellar structure and evolution (both of single and binary stars) in a broad range of masses, evolutionary stages, and chemical compositions, and as indicators of distance and time. With the numerous ongoing photometric surveys and upcoming space astrometry and photometry missions, the future of binaries looks bright. The various aspects of binaries as astrophysically useful laboratories are reviewed here, with emphasis on the currently open problems and research opportunities. 
Ignasi Ribas (CSIC, IEEC, Spain)