This paper proposes a new phenomenology for strong incompressible MHD turbulence with nonzero cross helicity. This phenomenology is then developed into a quantitative Fokker-Planck model that describes the time evolution of the anisotropic power spectra of the fluctuations propagating parallel and antiparallel to the background magnetic field image. It is found that in steady state the power spectra of the magnetic field and total energy are steeper than image and become increasingly steep as image increases, where image is the cross helicity, image is the fluctuation energy, and image is the wavevector component perpendicular to image. Increasing C with fixed image increases the time required for energy to cascade to smaller scales, reduces the cascade power, and increases the anisotropy of the small-scale fluctuations. The implications of these results for the solar wind and solar corona are discussed in some detail.