Earth's solid inner core and surrounding liquid outer core exist at the most extreme conditions in our planet. Despite its inaccessibility, collaborative efforts from observations, experiments, theory, and simulations reveal a wealth of dynamic phenomena in the core. The core is comprised mostly of iron, and the contested cocktail of alloying elements are critical for determining geodynamo behavior, as they help power convection and affect physical and transport properties. Observations document seismic anisotropy in the inner core and the presence of layers within outer core, but their causes and consequences are open to interpretation. Addressing such outstanding questions is key to understanding our planet beyond the core, from the lower mantle to the magnetosphere, as well as temporally, from Earth's formation to present. We thus encourage contributions from disciplines such as seismology, mineral physics, geochemistry, geodynamics, and geomagnetism, in order to develop a holistic picture of the Earth's metallic heart.