This book provides a systematical and comprehensive description of some facets of modeling, designing, analyzing and exploring the control allocation and fault-tolerant control problems for over-actuated spacecraft attitude control system under actuator failures, system uncertainties and disturbances. The book intends to provide a unified platform for understanding and applicability of the fault-tolerant attitude control and control allocation for different purposes in aerospace engineering and some related fields. And it is particularly suited for readers who are interested to learn solutions in spacecraft attitude control system design and related engineering applications.