U-Spin Symmetry in Charmless B Decays

We prove a general theorem about equal CP rate differences within pairs of U-spin related charmless $B$ and $B_s$ decays. Large deviations from equalities would be evidence for new physics. Six pairs of decays into two pseudoscalar mesons are identified where such relations hold. Ratios of corresponding rate differences and certain ratios of rates measure U-spin breaking. These processes provide useful information on the weak phase $\gamma={\rm Arg} V^*_{ub}$. Applications of U-spin symmetry to other decays are discussed.