Abstract

About 20 percent of all detected exoplanets inhabit multiple star systems and several observational campaigns are now actively searching for planets in binary stars. This has fueled a renewed interest in studies of planet formation in multiple star systems. Some issues, such as the long term stability of planets in binaries or how binarity affects the last stages of the planet formation process (from embryos to planets) are now relatively well understood. However, other issues are still actively debated, in particular regarding the crucial early stage leading from km-sized planetesimals to embryos. The main question is here if the coupled effect of gas drag, companion star perturbations and mutual collisions favours, hinders or simply does not affect planetesimal accretion. I will review the latest studies on this complex problem, with a specific focus on 2 individual systems: Gamma Cephei, the most famous binary system with a detected exoplanet, and alpha Centauri, the most famous binary system that might harbour a terrestrial planet.