  Tremendous progress has been achieved in neutrino oscillation physics during
the last few years. However, the smallness of the $\t13$ neutrino mixing angle
still remains enigmatic. The current best constraint comes from the CHOOZ
reactor neutrino experiment $\s2t13 < 0.2$ (at 90% C.L., for $\adm2=2.0 10^{-3}
\text{eV}^2$). We propose a new experiment on the same site, Double-CHOOZ, to
explore the range of $\s2t13$ from 0.2 to 0.03, within three years of data
taking. The improvement of the CHOOZ result requires an increase in the
statistics, a reduction of the systematic error below one percent, and a
careful control of the cosmic ray induced background. Therefore, Double-CHOOZ
will use two identical detectors, one at $\sim$150 m and another at 1.05 km
distance from the nuclear cores. The plan is to start data taking with two
detectors in 2008, and to reach a sensitivity of 0.05 in 2009, and 0.03 in
2011.
