  The wavelength-dependence of the extinction of Type Ia SN2014J in the nearby
galaxy M82 has been measured using UV to near-IR photometry obtained with the
Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu
Infrared Telescope. This is the first time that the reddening of a SN Ia is
characterized over the full wavelength range of $0.2$-$2$ microns. A
total-to-selective extinction, $R_V\geq3.1$, is ruled out with high
significance. The best fit at maximum using a Galactic type extinction law
yields $R_V = 1.4\pm0.1$. The observed reddening of SN2014J is also compatible
with a power-law extinction, $A_{\lambda}/A_V = \left( {\lambda}/ {\lambda_V}
\right)^{p}$ as expected from multiple scattering of light, with
$p=-2.1\pm0.1$. After correction for differences in reddening, SN2014J appears
to be very similar to SN2011fe over the 14 broad-band filter light curves used
in our study.
