In astronomy and cosmology, dark fluid is an alternative theory to both dark matter and dark energy and attempts to explain both phenomena in a single framework.

Dark fluid proposes that dark matter and dark energy are not separate physical phenomena as previously thought, nor do they have separate origins, but that they are linked together and are really specific sub-effects of new extended laws of gravity at very large scales. Other alternative theories of extended gravity, such as Modified Newtonian dynamics (MOND), also show up as specific sub-effects. Our current laws of gravity modeled on observations within the scales of the Earth and the Solar System might be insufficient to explain gravity at these larger scales.