The formation of the first supermassive black holes is one of the main open questions in our understanding of high-redshift structure formation. In this book, we aim to provide a summary of state-of-the-art modern research on this topic, exploring the formation of massive black holes from a fluid-dynamical, stellar-dynamical and chemical perspective. The book thus provides a solid theoretical foundation and a comparison with current observations and future perspectives, including modern topics such as the potential of the Square Kilometre Array, the European Extremely Large Telescope, the Euclid satellite and possible detections via gravitational waves.