Yao and Padgett (2011) review the origins, behavior, and applications of orbital angular momentum (OAM) in light. OAM arises from the helical phase structure of light beams, which can carry much larger angular momentum than spin angular momentum (SAM). These beams, with optical vortices along their axis, can be easily generated in the lab and have applications in manipulating microscopic objects, creating new imaging systems, and enabling quantum optics experiments. The paper discusses the generation of OAM beams using spiral phase plates, Laguerre-Gaussian modes, and diffractive optical elements. It also explores the interaction of OAM beams with matter, including their ability to rotate particles, induce rotational frequency shifts, and interact with cold atoms. The paper highlights the use of OAM in nonlinear and quantum optics, such as in parametric down conversion and quantum entanglement. It also addresses the measurement of OAM, the role of coherence in OAM beams, and the extension of OAM beyond light to other waveforms like radio waves and electron beams. The paper concludes with reflections on the significance of OAM and future opportunities in its application.Yao and Padgett (2011) review the origins, behavior, and applications of orbital angular momentum (OAM) in light. OAM arises from the helical phase structure of light beams, which can carry much larger angular momentum than spin angular momentum (SAM). These beams, with optical vortices along their axis, can be easily generated in the lab and have applications in manipulating microscopic objects, creating new imaging systems, and enabling quantum optics experiments. The paper discusses the generation of OAM beams using spiral phase plates, Laguerre-Gaussian modes, and diffractive optical elements. It also explores the interaction of OAM beams with matter, including their ability to rotate particles, induce rotational frequency shifts, and interact with cold atoms. The paper highlights the use of OAM in nonlinear and quantum optics, such as in parametric down conversion and quantum entanglement. It also addresses the measurement of OAM, the role of coherence in OAM beams, and the extension of OAM beyond light to other waveforms like radio waves and electron beams. The paper concludes with reflections on the significance of OAM and future opportunities in its application.