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. 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.