Gravitational waves are ripples in the fabric of spacetime, predicted by Einstein's theory of general relativity. eLISA is a space-based gravitational wave observatory that can detect and study these gravitational waves. It is a joint project of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). eLISA is designed to detect gravitational waves from astronomical sources such as merging black holes and neutron stars. It would use laser interferometry to measure the tiny distortions in spacetime caused by passing gravitational waves. Detecting gravitational waves would provide important insights into the nature of gravity and the evolution of the universe.