Polarization carries information about the geometry and structure of the magnetic field
in blazars jets, as seen by the emitting particles.
So far such studies were possible only from radio to optical frequencies.
With the advent of IXPE, it is now possible to measure
linear polarization in the X-ray band for several type of blazars.
In high-energy-peaked blazars the X-ray band is fully dominated by the synchrotron emission
of freshly accelerated electrons.
Since X-ray electrons cool much faster then optical electrons, IXPE is probing
the structure of the magnetic field on smaller scales and closer to the acceleration sites.
Here I give an overview of the first IXPE observations of blazars, discussing the results
in the context of their SED.