In 2004, the idea that a long-lived form of spin order, namely singlet order, can be prepared from nuclear spin magnetisation emerged. This first book on the subject gives a thorough description of the various aspects that intervene in the development of the topic and details the interdisciplinary applications. The book starts with a section dedicated to the basic theories of long-lived spin order and then proceeds with a description of the state-of-the-art experimental techniques developed to manipulate singlet order. The book proceeds by describing several applications of this order in various fields of research and then concludes by covering the generalization of the concept of singlet order by introducing and discussing other forms of long-lived spin order. This idea has caught the attention of research groups interested in exploiting this form of order in different fields of research spanning from biology to materials science and from hyperpolarisation to quantum computing.