Blazars (Active Galactic Nuclei with the relativistic jet pointing towards us)
are among the most powerful persistent gamma-ray sources in the Universe.
Yet the origin and mechanism of their emission remain elusive,
despite the large increase of data collected in the last years.
Results from Fermi-LAT and atmospheric Cherenkov telescopes
are starting to question several aspects of the standard picture.
I will discuss some of these issues, and in particular the location of the
gamma-ray emission, the FSRQ/BLLac classification, the ultra-fast
variability and the hard TeV objects.