Earth's mantle is integral to many processes that shape our planet, including convection, crustal formation, crustal recycling, and global heat and volatile budgets. Still, many questions remain unresolved about mantle composition and its influence on geodynamics today and throughout geologic time. Because they originate at depths that can extend to the core-mantle boundary, mantle plumes provide invaluable information about the composition of the deep mantle. In this review, we discuss the effectiveness and challenges of using isotopic analyses of plume-derived rocks to document the origin and composition of mantle heterogeneities, earlyformed mantle reservoirs, crustal recycling processes, core-mantle interactions, and mantle evolution. We discuss isotopic methods and improvements to existing isotopic systems to characterize plume-derived ocean island basalts. Nevertheless, because mantle plumes vary in many properties, including magmatic flux, temperature, tectonic environment, and compositions, geochemical observations on plume-generated systems must be considered carefully before making interpretations about Earth's interior. Consequently, plumes and their melts should be evaluated along a spectrum that acknowledges and contextualizes their differences, particularly mantle flux. Ultimately, the most important advancements in mantle geochemistry, architecture, and dynamics will emerge from cross-disciplinary studies in diverse fields such as experimental petrology, mineral physics, numerical geodynamics, seismology, and geochemistry.