Chemical differentiation has been shaping the Earth´s crust through endless cycles of re-melting and melt migration over the last 4 billion years. Small portions of this melt can survive as inclusions called “nanogranitoids”, sheltered in the most refractory metamorphic minerals of partially melted rocks, i.e. migmatites. A precise knowledge of the crustal melt chemistry and its mechanisms of melt production are necessary to precisely understand both chemical and geodynamic evolution of our planet. The study of melt inclusion in metamorphic rocks provides exactly this: natural partial melts can be characterized in detail, including their water, carbon dioxide and halogen (e.g. chlorine) content directly in natural rocks, melt-producing reactions can be directly identified and previously unrecognized re-melting events discovered. As a novel field of study, its development necessarily leads to unexpected findings, such as rare mineral phases or new crucial insights into the role of crustal melting in crust-mantle interaction during crustal subduction. A more complete portrait of the behaviour of melts, fluids and crustal evolution lays ahead on the road of nanogranitoids investigation.