  Electron transport in mesoscopic conductors has traditionally involved
investigations of the mean current and the fluctuations of the current. A
complementary view on charge transport is provided by the distribution of
waiting times between charge carriers, but a proper theoretical framework for
coherent electronic systems has so far been lacking. Here we develop a quantum
theory of electron waiting times in mesoscopic conductors expressed by a
compact determinant formula. We illustrate our methodology by calculating the
waiting time distribution for a quantum point contact and find a cross-over
from Wigner-Dyson statistics at full transmission to Poisson statistics close
to pinch-off. Even when the low-frequency transport is noiseless, the electrons
are not equally spaced in time due to their inherent wave nature. We discuss
the implications for renewal theory in mesoscopic systems and point out several
analogies with energy level statistics and random matrix theory.
