Coral reefs are important marine ecosystems, supporting immense biodiversity and providing significant ecological and economic benefits. Corals and the reefs they build face unprecedented decline from local and global anthropogenic pressure. Central to the health and resilience of coral reefs is the coral microbiome, a complex community of microorganisms that inhabit coral tissues, mucus, skeleton, and the surrounding environment. Microbial communities play a critical role in maintaining coral health, mediating nutrient cycling, and enhancing stress tolerance. Besides host-associated microbes, environmental microorganisms shape the reef ecosystem and its functions. The importance of host- and ecosystem-associated microbiomes, our ability to alter their structure and function, and the ongoing decline of coral reefs led to the notion of ‘microbiome stewardship’, i.e. the management of the microbiome to restore/rehabilitate organisms and ecosystem function, increase resilience, and counter biodiversity loss. This book starts with dedicated chapters to detail the most important microbial associates of corals. It then outlines the emergent coral holobiont and the underlying structuring forces to subsequently transition over to ecosystem-scale microbiology and health of coral reefs. After that, the book explores how microbial processes contribute to coral disease, highlights microbial therapies for restoring coral health, and provides a roadmap for their implementation. The book concludes with a discussion on coral microbiome biotechnology and a forward-looking perspective on enhancing coral reef restoration through adaptive interventions and data science under a One-Health concept. This chapter provides an introduction to the book, briefly highlighting the various chapters.