  Periodic solutions of the three body problem are very important for
understanding its dynamics either in a theoretical framework or in various
applications in celestial mechanics. In this paper we discuss the computation
and continuation of periodic orbits for planetary systems. The study is
restricted to coplanar motion. Staring from known results of two-planet systems
around single stars, we perform continuation of solutions with respect to the
mass and approach periodic orbits of single planets in two-star systems. Also,
families of periodic solutions can be computed for fixed masses of the
primaries. When they are linearly stable, we can conclude about the existence
of phase space domains of long-term orbital stability.
