Hexagonal boron nitride (hBN) exhibits unique optical properties in the deep-UV region, along with exceptional mechanical robustness, thermal stability, and chemical inertness. These characteristics have driven significant interest in hBN thin films for applications in nanoelectronics, photonics, single-photon emission, anti-corrosion coatings, and membranes. Achieving wafer-scale, thickness-controlled growth of hBN is crucial for enabling its industrial-scale integration. While extensive efforts have been made to develop continuous hBN thin films with high crystallinity, ranging from large-grain polycrystalline films to single crystals, precise thickness control over wafer-scale dimensions remains a challenge. The growth of hBN is highly dependent on the substrate, particularly the type of metal catalysts, as the solubility of boron and nitrogen varies across different metals. In this talk, I will summarize state-of-the-art strategies for achieving wafer-scale, thickness-controlled hBN growth and discuss the underlying growth mechanisms on catalytic substrates. Furthermore, I will present recent advancements in growing hBN films directly on dielectric, sapphire substrate. Finally, I will demonstrate some applications of hBN in next-generation Li metal batteries, proton transport membranes, and quantum emitters.