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, $R_Vgeq3.1$, is ruled out with high significance. The best fit at maximum using a Galactic type extinction law yields $R_V = 1.4pm0.1$. 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 $p=-2.1pm0.1$. 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.
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