The outskirts of galaxy clusters are the regions where matter accretes from the large-scale structure onto the most massive halos, and as such they are important for the understanding of structure formation processes. However, due to the steep decrease of the X-ray signal with radius their study has been challenging for X-ray satellites, leading to several controversial results. Recently, Planck detected the imprint of the Sunyaev-Zeldovich effect beyond the virial radius in a large sample of galaxy clusters. Combining the Planck data with a set of archival observations from ROSAT/PSPC, we were able for the first time to study the thermodynamics and the composition of clusters in their entire volume in a relatively large cluster sample. I will present in particular our results on the radial profiles of temperature, entropy, and gas fraction, and discuss the implications of these results for astrophysics and cosmology.