  The preponderance of binary systems in all known stellar populations makes
them exciting dynamical agents for research on topics as varied as star
formation, star-cluster dynamics and the interiors of young and old stars.
Today we know that the Galactic-field binary population is probably a
dynamically evolved version of the Taurus-Auriga pre-main sequence population,
and that the initial distributions of binary-star orbital elements are probably
universal. Furthermore, N-body calculations tentatively suggest that OB stars
form in energetic binaries near cluster cores, and that binaries with
'forbidden' orbital elements that are produced in stellar encounters, may turn
out to be very useful windows into stellar interiors, potentially allowing
tests of pre-main sequence evolution theory as well as of models of
main-sequence stars.
