  The field of the globular cluster M22 (NGC 6656) was monitored between 2000
and 2008 in a search for variable stars. $BV$ light curves were obtained for
359 periodic, likely periodic, and long-term variables, 238 of which are new
detections. Thirty nine newly detected variables, and 63 previously known ones
are members or likely members of the cluster, including 20 SX Phe, 10 RRab and
16 RRc-type pulsators, one BL Her-type pulsator, 21 contact binaries, and 9
detached or semi-detached eclipsing binaries. The most interesting among the
identified objects are V112 - a bright multimode SX Phe pulsator, V125 - a
$\beta$ Lyr-type binary on the blue horizontal branch, V129 - a blue/yellow
straggler with a W UMa-like light curve, located halfway between the extreme
horizontal branch and red giant branch, and V134 - an extreme horizontal branch
object with $P=2.33$ d and a nearly sinusoidal light curve; all four of them
are proper motion (PM) members of the cluster. Among nonmembers, a $P=2.83$ d
detached eclipsing binary hosting a $\delta$ Sct-type pulsator was found, and a
peculiar $P=0.93$ d binary with ellipsoidal modulation and narrow minimum in
the middle of one of the descending shoulders of the sinusoid. We also
collected substantial new data for previously known variables; in particular we
revise the statistics of the occurrence of the Blazhko effect in RR Lyr-type
variables of M22.
