  The time delays between point-like images in gravitational lens systems can
be used to measure cosmological parameters. The number of lenses with measured
time delays is growing rapidly; the upcoming \emph{Large Synoptic Survey
Telescope} (LSST) will monitor $\sim10^3$ strongly lensed quasars. In an effort
to assess the present capabilities of the community to accurately measure the
time delays, and to provide input to dedicated monitoring campaigns and future
LSST cosmology feasibility studies, we have invited the community to take part
in a "Time Delay Challenge" (TDC). The challenge is organized as a set of
"ladders," each containing a group of simulated datasets to be analyzed blindly
by participating teams. Each rung on a ladder consists of a set of realistic
mock observed lensed quasar light curves, with the rungs' datasets increasing
in complexity and realism. The initial challenge described here has two
ladders, TDC0 and TDC1. TDC0 has a small number of datasets, and is designed to
be used as a practice set by the participating teams. The (non-mandatory)
deadline for completion of TDC0 was the TDC1 launch date, December 1, 2013. The
TDC1 deadline was July 1 2014. Here we give an overview of the challenge, we
introduce a set of metrics that will be used to quantify the goodness-of-fit,
efficiency, precision, and accuracy of the algorithms, and we present the
results of TDC0. Thirteen teams participated in TDC0 using 47 different
methods. Seven of those teams qualified for TDC1, which is described in the
companion paper II.
