  We recently commissioned the polarimetric upgrade of the HARPS spectrograph
at ESO's 3.6-m telescope at La Silla, Chile. The HARPS polarimeter is capable
of full Stokes spectropolarimetry with large sensitivity and accuracy, taking
advantage of the large spectral resolution and stability of HARPS. In this
paper we present the instrument design and its polarimetric performance. The
first HARPSpol observations show that it can attain a polarimetric sensitivity
of ~10^-5 (after addition of many lines) and that no significant instrumental
polarization effects are present.
