  We discuss the potential of the proposed Double Chooz reactor experiment to
measure the neutrino mixing angle $\sin^2 2\theta_{13}$. We especially consider
systematical uncertainties and their partial cancellation in a near and far
detector operation, and we discuss implications of a delayed near detector
startup. Furthermore, we introduce Triple Chooz, which is a possible upgrade
scenario assuming a second, larger far detector, which could start data taking
in an existing cavern five years after the first far detector. We review the
role of the Chooz reactor experiments in the global context of future neutrino
beam experiments. We find that both Double Chooz and Triple Chooz can play a
leading role in the search for a finite value of $\sin^2 2\theta_{13}$. Double
Chooz could achieve a sensitivity limit of $\sim 2 \cdot 10^{-2}$ at the
90%~confidence level after 5~years while the Triple Chooz setup could give a
sensitivity below $10^{-2}$.
