  The current understanding of the origin of barium and S stars is reviewed,
based on new orbital elements and binary frequencies. The following questions
are addressed: (i) Is binarity a necessary condition to produce a barium star?
(ii) What is the mass transfer mode (wind accretion or RLOF?) responsible for
their formation? (iii) Do barium stars form as dwarfs or as giants? (iv) Do
barium stars evolve into Tc-poor S stars? (v) What is the relative frequency of
Tc-rich and Tc-poor S stars?
