This chapter reviews the evolution of al-Qaida from 1988–2020 in the context of political scientist David Rapoport’s “wave” theory. It argues that al-Qaida has experienced four historical waves of activity since its formation more than three decades ago, measured by the number of fatalities from its attacks globally. The chapter revisits al-Qaida’s establishment in 1988 and then provides background on key moments in the group’s progression through the decades. It finds that while al-Qaida has conducted a number of successful terrorist attacks, the group is no closer today to achieving its ambitious goal of a pan-Islamic caliphate. The group has failed to hold territory, and it has been unable to increase its popular support in the Muslim world.