This paper provides a stateoftheart overview on the melt morphology and distribution in partially molten rocks under hydrostatic and dynamic conditions with special focuses on the influence of partial melting on rheological behavior of peridotite and granite. Partial melting controls most of the important geological processes (e.g., formation of the crust, compositional evolution of the mantle) and the physical properties of deep crust and upper mantle (e.g., electrical conductivity, anelasticity, seismic wave velocities, and permeability). The understanding of the rheological properties of partially molten rocks is thus essential for modeling precisely largescale geological processes including mechanical coupling between the crust and lithospheric mantle, convection of asthenosphere, plate tectonics, channel flow of middle to lower crust, mountainbuilding mechanisms. Significant progress in both experimental and theoretical studies occurred during the last three decades and has promoted our understanding of the rheological properties of partially molten rocks. The following consensus has been reached: under hydrostatic conditions, melt whose volume fraction is less than ~2% is generally restricted to the triple junctions or along grain edges. The degree of melt wetting increases with increasing pressure, temperature and melt fraction. Under nonhydrostatic conditions (either coaxial compression or simple shear), however, melt occurs predominantly along extensional shear bands aligned at angles of about 15°~ 30° to the maximum principal compressive stress. The presence of <5% melt results hence in only a modest rheological weakening due to the heterogeneous distribution of melt. With increasing the melt fraction, the partially molten rocks are significantly weakened, which leads to deformationinduced melt segregation or extraction.