Gravitational Wave (GW) observatories are humanity’s newest tool for studying the universe. After decades of development efforts, terrestrial interferometers such as LIGO and Virgo are now routinely detecting ripples in the fabric of spacetime caused by distant astrophysical cataclysms such as the collision of black holes. Early results from these instruments have already provided answers to long-standing questions in astrophysics and, more importantly, introduced new questions of their own. However, even as instruments on the Earth continue to improve, there will be vast portions of the GW spectrum that will not be accessible due to their limited size and noise in the terrestrial environment. Space-based interferometers a million times larger than their terrestrial cousins will probe the milliHertz GW spectrum, home to a rich variety of astrophysical signals. In this talk, I will provide an overview of the Laser Interferometer Space Antenna (LISA), an international collaboration to develop the first space-based GW interferometer. I will describe the science applications, the mission concept, and key technologies behind what will be the largest scientific instrument ever constructed. I will also highlight the contributions of LISA Pathfinder, a European-led technology demonstration mission that validated several critical aspects of the LISA concept.