here is one key prediction of GR that has not yet been observed directly: The non-linearity of gravity implies that the energy-momentum carried by gravitational waves themselves acts as a source of spacetime modifications. As a consequence, any gravitational wave emission ought to come with an additional source of radiation that manifests itself as a DC component within the gravitational wave signal. This is known as the gravitational wave memory effect. Exitingly, the planned space-based GW observatory LISA might however provide us with the first discovery of GW memory. After offering a particularly illuminating theoretical foundation of GW memory, this talk will cover a recent analysis of its expected signature within LISA and discuss the potential lessons to be learned from directly measuring the non-linearity of gravity. Based on: JZ, Lavinia Heisenberg, Nicolás Yunes, “Gravitational wave memory beyond general relativity”, Phys.Rev.D 108 (2023) 2, 024010, https://arxiv.org/abs/2303.02021 JZ, Guangzi Xu, Lavinia Heisenberg, “Unifying ordinary and null memory”, JCAP 05 (2024) 119, https://arxiv.org/abs/2401.05936 Henri Inchauspé, JZ, et al. , “Measuring gravitational wave memory with LISA”, (2024), https://arxiv.org/abs/2406.09228