A Comprehensive Guide to Angular Momentum begins by considering substantiations of the theorem of angular momentum change and the law of conservation of angular momentum, as the change of angular momentum indicates an error in the method of calculating the dynamics of the Solar system. Following this, different techniques for the analysis of the orbital angular momentum of electromagnetic fields are reviewed and discussed, describing their main advantages and disadvantages, and providing key ready-to-use methods for detection. The concluding chapter provides a theoretical explanation of photonic orbital angular momentum and explains its distinction from atomic orbital angular momentum. Global conservation of angular momentum implies that light must transfer not only its spin, but also its orbital angular momentum in order to matter.