A review of the densification mechanisms and the microstructural development for transparent spinel made by free sintering and by hot pressing is given. The paper is divided into two main parts. The first part considers spinel without any sintering additives because there still is some controversy concerning the role of cation stoichiometry on sintering and grain growth. The second part discusses the role of the classic sintering aid, LiF, in processing transparent spinel. LiF is shown to have multiple behaviors: (1) it initially wets spinel and forms a liquid phase at relatively low temperatures, which affects early-stage densification and also grain growth; (2) upon cooling from intermediate temperatures, or even from higher temperatures if microstructure evolution (e.g., formation of closed porosity) prevents volatization, the LiF-containing liquid dewets and resides in isolated pockets; (3) LiF alters the cation stoichiometry, thereby enhancing diffusion via an increase in the concentration of oxygen vacancies; this affects both the densification rate and grain growth; and (4) it reacts with impurities in the system, thereby acting as a cleanser. For the production of transparent spinel, it is critical that LiF or associated reaction products not be retained as a secondary phase.