  B meson decays involving b -> u transitions are sensitive to the unitarity
triangle angle alpha (or phi2). The BaBar and Belle experiments have studied
B-meson decays to pipi, rhopi and rhorho final states. It is possible to
combine these measurements to constrain alpha with a precision of O(10 degrees)
and a central value of approximately 100 degrees. These results are consistent
with Standard Model expectations.
