This chapter will discuss the development history, recent progress, and technical principles of HVPE. HVPE is a crucial technique for synthesizing bulk single crystals of AlN with high ultraviolet transmittance. However, achieving heteroepitaxial growth of AlN on foreign substrates with lattice and thermal mismatches (such as SiC and sapphire) remains a challenge, often leading to defect formation and crack propagation. Advanced strategies, such as multi-step epitaxial growth, high-temperature annealing of buffer layer, and the use of patterned substrates, have proven effective in reducing dislocation densities and minimizing cracking. Void-assisted self-separation enables the production of crack-free, freestanding AlN substrates. Furthermore, HVPE homoepitaxy on PVT-grown AlN substrates yields high-quality AlN single crystals with extremely low dislocation densities and enhanced deep-UV transparency. Recent advancements have demonstrated AlN growth rates exceeding 150 µm/h through the use of high-temperature HVPE and the suppression of gas-phase pre-reactions. These advancements establish HVPE-AlN as a cornerstone for deep-UV optoelectronics and high-power electronic device.