There is a growing consensus that avoiding dangerous levels of climate change requires reaching net-zero emissions globally by the middle of the twenty-first century. Industrial decarbonization is the least studied and understood element of the deep decarbonization challenge, despite the fact that several industrial sectors are among the toughest to decarbonize. Among industrial sectors, three stand out as particularly difficult to decarbonize: steel, cement, and petrochemicals. Combined, these sectors are responsible for nearly a fifth of global carbon dioxide emissions and a quarter of industrial CO2 emissions. This chapter introduces industrial decarbonization and discusses the difficulties because most industrial processes release CO2 as an intrinsic part of chemical reactions inherent in the process. These are called process emissions. Many other industrial processes emit fossil CO2 as a by-product of providing the high temperature or pressure heat needed for the reactions. Collectively, these are energy-related or indirect industrial emissions. There is no single decarbonization solution for these sectors. These three sectors differ in the importance of direct and indirect emissions, their unique challenges, and the potential costs and resource requirements for different technology pathways. As a result, identifying emission reduction pathways in these difficult sectors is vital for avoiding the kinds of investments that could lock the world into a high-emission trajectory despite climate change mitigation efforts already well underway. Only once it is known what it would take to decarbonize those materials can industry-backed climate policies be developed and relevant stakeholders be engaged.