The effect of B doping on the surface (111) reactivity has, in the present study, been investigated for various surface terminations, H, OH, Oon-top, and F. This type of surface modification has experimentally been proven to be extremely important for, for example, applications based on surface electrochemistry. Density functional theory (DFT) has here been used to study both the local and more global effects of substitutionally positioned B atoms in the upper part of the diamond (111) surface. For this purpose, adsorption energies for the various terminating species have been calculated, and the observed results have been carefully analyzed in order to gain a deeper knowledge about the atomic-level cause of the observed effects. As a result, the B dopant shows a clear, but local, effect for all terminating species investigated. In addition, it is only the radical O-terminating species that show a special and high reactivity on the diamond surface. The other terminating species show a much lower reactivity, which in addition are very similar.