  We report time-series photometry for 55 variable stars located in the central
part of the globular cluster M55. The sample includes 28 newly identified
objects of which 13 are eclipsing binaries. Three of these are detached systems
located in the turn-off region on the cluster color-magnitude diagram. Two of
them are proper motion (PM) members of M55 and are excellent candidates for a
detailed follow-up study aimed at a determination of the cluster age and
distance. Other detached binaries are located along the unevolved part of the
cluster main sequence. Most of the variables are cluster blue straggler stars.
This group includes 35 SX Phe stars, two contact binaries, and one
semi-detached binary. V60 is a low mass, short period algol with the less
massive and cooler component filling its Roche lobe. The more massive component
is an SX Phe variable. The orbital period of V60 increases at a rate of
dP/P=3.0E-9. In addition to numerous variable blue stragglers we also report
the detection of two red stragglers showing periodic variability. Both of these
are PM members of M55. We note and discuss the observed paucity of contact
binaries among unevolved main sequence stars in M55 and NGC 6752. This apparent
paucity supports an evolution model in which the formation of contact binaries
is triggered by stellar evolution at the main-sequence turn off.
