  The first calibrated broadband UBVI time-series photometry is presented for
the RR Lyrae variable stars in NGC6656 (M22), with observations spanning a
range of twenty-two years. We have also redetermined the variability types and
periods for the RR Lyrae stars identified previously by photographic
observations, revising the number of fundamental-mode RR Lyrae variables (RR0)
to 10 and the number of first-overtone variables (RR1) to 16. The mean periods
of the RR0 and RR1 variables are <P>_{RR0}=0.66 \pm 0.02 d and <P>_{RR1}=0.33
\pm 0.01 d, respectively, supporting an Oosterhoff II classification for the
cluster. The number ratio of RR1- to all RR-type variables is N_1/N_{RR}=0.61,
also consistent with an Oosterhoff II designation. Both the RR Lyrae stars'
minimum light colors and the blue edge of the RR Lyrae instability strip
suggest E(B-V)=0.36 \pm 0.02 mag toward M22. Regarding the HB morphology of
M22, we find (B-R)/(B+V+R)=+0.97 \pm 0.1 and at least one "gap" located in an
unusual part of the blue HB, in the middle of the so-called hot HB stars.
