  We present accurate photometric redshifts in the 2-deg2 COSMOS field. The
redshifts are computed with 30 broad, intermediate, and narrow bands covering
the UV (GALEX), Visible-NIR (Subaru, CFHT, UKIRT and NOAO) and mid-IR
(Spitzer/IRAC). A chi2 template-fitting method (Le Phare) was used and
calibrated with large spectroscopic samples from VLT-VIMOS and Keck-DEIMOS. We
develop and implement a new method which accounts for the contributions from
emission lines (OII, Hbeta, Halpha and Ly) to the spectral energy distributions
(SEDs). The treatment of emission lines improves the photo-z accuracy by a
factor of 2.5. Comparison of the derived photo-z with 4148 spectroscopic
redshifts (i.e. Delta z = zs - zp) indicates a dispersion of sigma_{Delta
z/(1+zs)}=0.007 at i<22.5, a factor of 2-6 times more accurate than earlier
photo-z in the COSMOS, CFHTLS and COMBO-17 survey fields. At fainter magnitudes
i<24 and z<1.25, the accuracy is sigma_{Delta z/(1+zs)}=0.012. The deep NIR and
IRAC coverage enables the photo-z to be extended to z~2 albeit with a lower
accuracy (sigma_{Delta z/(1+zs)}=0.06 at i~24). The redshift distribution of
large magnitude-selected samples is derived and the median redshift is found to
range from z=0.66 at 22<i<22.5 to z=1.06 at 24.5<i<25. At i<26.0, the
multi-wavelength COSMOS catalog includes approximately 607,617 objects. The
COSMOS-30 photo-z enable the full exploitation of this survey for studies of
galaxy and large scale structure evolution at high redshift.
