  We present multi-color light curves for the W UMa-type eclipsing binary TU
Boo for two epochs separated by 22 years. An analysis of the O-C diagram
indicates the earlier observations took place right in the middle of a major
period change, thus allowing for a unique study on mass transfer and period
changes in this W UMa-type system. We compute model fits to our light curves,
along with the only other published set, using the Wilson-Devinney program, and
find temporally correlated changes in the size of the secondary component with
anomalies in the O-C diagram. We investigate the cause of these changes and
find support for the existence of rapid, large-scale mass transfer between the
components. We postulate that this interaction allows them to maintain nearly
equal surface temperatures despite having achieved only marginal contact. We
also find support for the evolutionary scenario in which TU Boo has undergone a
mass ratio reversal in the past due to large-scale mass transfer so that what
is presently the secondary component of TU Boo is in an advanced evolutionary
state, oversized due to a helium-enriched core, with a total system age of
$\geq$ 10 Gyr.
