While gathering measurements of the primary CMB anisotropies, the ESA Planck
satellite is also collecting unique and
unprecedented data for a wide range of foreground sources. This includes a blind
all-sky survey of galaxy clusters
detected through the thermal Sunyaev-Zel'dovich effect (inverse Compton scattering
of CMB photons interacting with free electrons in the hot intra-cluster plasma).
In the talk I will describe the basic properties of the survey and the resulting
cluster sample, and discuss how
it can yield significantly improved cosmological constraints on e.g. dark energy and
neutrino mass
compared to previous X-ray and ground-based SZ cluster surveys. In addition, I will
discuss recent results on the properties
of the Planck-detected clusters, as revealed by multi-wavelength follow-up
observations from space and from the ground.