  The observation and measurement of missing transverse energy in an event is a
key signature in SUSY searches. This paper describes the reconstruction and
calibration of missing transverse energy in ATLAS, and addresses the quality of
the measurement in a variety of simulated processes which contain physical
missing transverse energy such as $Z$ $\to$ $\tau^{+}\tau^{-}$, $A^{0}$ /
$H^{0}$ $\to$ $\tau^{+}\tau^{-}$, $t$$\bar{t}$, and SUSY as well as processes
which contain no missing transverse energy such as minimum bias and $Z$+jets.
Expectations for the use of early data in evaluation of the measurement of
missing transverse energy are presented.
