Ground magnetometer observations have played a major role in the development of space science, by remotely measuring currents that define the dynamics of the magnetosphere and Earth's ionosphere. They have led to the identification of ionospheric currents associated with magnetic substorms and storms, as well as those associated with global compressions of the magnetosphere from interplanetary shocks and bow shock-related instabilities. Ground magnetometer observations have made it possible to track and comprehend the way reconfigurations of currents and convection are propagated globally after the magnetosphere is impacted by solar wind and/or interplanetary magnetic field dynamics. Global ground magnetometer observations provide the most fundamental and necessary context that needs to exist if any of the current and future missions are to provide new discovery science within the Near-Earth Environment. While their role as a continuous monitor and context-providing source is paramount, their continuous operation on a now-global scale provides the means for research science at the systems. The above overview of the magnetometers on space-based magnetometers are by no means intended to be complete, but is to illustrate the historic success of magnetometers and the contributions to our understanding of space physics and related fields.