  Observatory end-to-end science operations is the overall process starting
with a scientific question, represented by a proposal requesting observing
time, and ending with the analysis of observation data addressing that
question, and including all the intermediate steps needed to plan, schedule,
obtain, and process these observations. Increasingly complex observing
facilities demand a highly efficient science operations approach and at the
same time be user friendly to the astronomical user community and enable the
highest possible scientific return. Therefore, this process is supported by a
collection of tools. In this paper, we describe the overall end-to-end process
and its implementation for the three upcoming extremely large telescopes
(ELTs), ESO's ELT, the Thirty Meter Telescope (TMT), and the Giant Magellan
Telescope (GMT).
