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Aluminum nitride is a covalently bonded III-V compound that combines high thermal conductivity with high electrical resistivity, and it is attractive where heat must be removed from a component that has to stay electrically insulated. The intrinsic lattice conductivity is high, and measurements on dense material established the baseline values against which later work is judged ^[1]; turning that into a commercial ceramic required control of the oxygen dissolved in the lattice, because the aluminium vacancies it creates scatter phonons and dominate the thermal resistance of a sintered body ^[2]. Oxide additions are what allow densification at practical temperatures, and they act by reacting with that dissolved oxygen to form an aluminate phase that removes the impurity from the grains, calcium oxide being the addition whose effect has been quantified most directly ^[3]. The residual grain-boundary film then sets both the thermal and the mechanical behaviour, so low-temperature routes are tuned to balance conductivity against strength ^[4]. Shaping by vat photopolymerisation is being developed for integrated packaging ^[5]. Bonding the ceramic to a metal substrate without introducing a thermal barrier remains the difficult step.