The ESA Planck satellite is dedicated to high precision measurements of the anisotropy and polarisation of the cosmic microwave background. Planck was launched from Kourou, French Guyana, on 14 May 2009 and since then it has been observing the sky continuously in nine frequency bands between 30 GHz and 857 GHz. The two Planck cryogenic instruments, based on radiometric and bolometric technologies, show very good performance and confirm the expectations from ground testing and calibration. The Planck wide spectral range, needed for precise subtraction of foreground components, provides at the same time an unprecedented source of new information for galactic and extragalactic mm-wave astrophysics. An overview will be given of the in-flight performance and of the first astrophysical results released in January 2011 by the Planck Collaboration based on the first year survey. Cosmological results are expected in 2013.