  The 5-year project Supernova Legacy Survey (SNLS) delivers $\sim 100$ Type-Ia
supernovae (SNe Ia) per year, in the redshift range $0.3 < z < 1.0$, with
well-sampled $g'r'i'z'$ lightcurves. The SNLS Collaboration uses the 1 deg$^2$
Megacam imager (36 $2048 \times 4612$ thinned CCDs) mounted on the 3.6-m
Canada-France-Hawaii Telescope (CFHT) to observe four fields around the sky, in
four filters. The primary goal of the project is to measure the dark energy
equation of state with a final statistical precision of $\pm 0.05$. We have
shown, using the first year dataset that the calibration uncertainties are
currently the dominant contribution to the systematic error budget. The
calibration of the SNLS dataset is challenging in several aspects. First,
Megacam is a wide-field imager, and only a handful of its 36 CCDs can be
directly calibrated using standard star observations. Second, measuring the
rest-frame $B$-band luminosity of SNe Ia over the $0.3<z<1.0$ redshift range
requires an excellent flux intercalibration of the Megacam bands. Finally, the
SN Ia SED differs significantly from that of stars and transfering the stellar
calibration to the SNLS data requires a precise knowledge of the SN Ia spectra
and the instrument transmissions. We present and discuss the SNLS calibration
strategy used to analyze the first year data set. We present the calibration
aspects which impact most the cosmological measurements. We also discuss the
intercalibration of the SNLS with other surveys, such as the CFHTLS-Wide and
the SDSS.
