Thermochemical water-splitting cycles use thermal energy to split water through several chemical reactions. The thermal energy required for water splitting in this method of hydrogen production can be either waste heat or from a nuclear power plant. This chapter is about the different thermochemical cycles, such as metal oxide-mediated cycles, three-step cycles, and the more complex multistep cycles, along with a brief historical backgroud, the reaction schemes, and operational conditions are described. Technologically more important cycles, such as the Cu–Cl cycle and UT-3 (Ca/Fe/Br) cycle, are discussed in more detail. Hybrid thermochemical cycles are studied for strategies to reduce operating temperatures and improve cyclic process efficiency, including the hybrid Cu–Cl, Westinghouse, and sulfur–ammonia (HySA) cycles. This chapter highlights the main challenges related to materials, efficiency, and scalability and outlines future perspectives for large-scale hydrogen production.