The Daya Bay Calibration System: Key to $\theta_{13}$

$\theta_{13}$, the only presently unknown neutrino mixing angle, can be measured via the disappearance of electron anti-neutrinos from nuclear reactors. Using this approach, the Daya Bay experiment aims to measure $\theta_{13}$ with an unprecedented sensitivity of $\sin^2(2\theta_{13})<0.01$. To reach the desired sensitivity, the detector properties need to be understood thoroughly, and a comprehensive calibration program is a must. In this talk, I will present the calibration system that is currently under construction, and discuss important detector-related systematics that can be controlled/reduced by the calibration program. I will tie these back into the sensitivity to $\theta_{13}$ at the end of the talk.