  The Planck satellite has proved to be a very successful mission, which has
been operating flawlessly for more than 36 months. Its main purpose is to map
the anisotropies of the CMB radiation at 9 frequencies, between 30 and 857 GHz,
with unprecedented resolution and sensitivity. After a description of the
properties and cosmological aims of Planck, we review the results obtained
during the first 1.6 full sky surveys relative to compact extragalactic sources
and their implications. The most recent and efficient methods and filters for
compact source detection in the presence of Gaussian noise and CMB anisotropies
are discussed. The first surveys of Planck have enabled the detection of about
200 galaxy clusters, by the SZ effect, and from several hundreds to many
thousands of extragalactic point sources (EPS), presented in the Planck ERCSC.
We review the results on the SZ effect in galaxy clusters. We discuss the
possibilities of future Planck data to study clusters through the SZ effect and
the interesting possibilities of combining these data with X ray observations.
These EPS can be classified into two main source classes: radio sources, at
intermediate to high z; far IR sources, typically at very z. Planck number
counts of EPS at LFI frequencies are in agreement with WMAP counts. A clear
steepening of the mean spectral index of bright radio sources is observed above
70 GHz, that can be interpreted in terms of a break frequency in their spectra.
For nearby dusty galaxies, Planck observations find evidence of colder dust,
with T < 20 K, than has previously been found. More recently, the number counts
of bright local dusty galaxies and of synchrotron sources have been measured by
Planck at submm wavelengths. Planck has provided interesting results on the
angular distribution of CIB anisotropies, allowing us to put new constraints on
clustering properties of dusty galaxies at high z.
