The nature of multiferroic surfaces, more specifically, the energetic, ferroelectric, and noncollinear magnetic properties of BiFeO3 (110) surfaces, is investigated using ab initio (first-principles) calculations based on the fully unconstrained spin-density functional theory. As in the case of other perovskite oxides, the O-terminated surface is found to be energetically favorable. The spontaneous polarization and magnetic moment at the surface rotate in different ways from their counterparts in the bulk, which leads to a unique magnetoelectric response at the surface. The detailed lattice-distortion-mode (symmetry) analysis reveals that the rotation of the ferroelectric polarization results from the additional symmetry breaking due to the surface termination, whereas the rotation of the magnetic moment is predominantly caused by the magnetocrystalline anisotropy. Furthermore, we investigate the effect of epitaxial strain and find that the strain responses of both the polarization and the magnetic moment are markedly enhanced at the surfaces.