This chapter surveys the evolution of democratization theory from the post–Cold War “transition paradigm” to more differentiated understandings of hybrid regimes, diverse trajectories, and democratic reversals. It begins by tracing the optimism of wave-based models, which assumed linear movement toward democracy, and shows how subsequent critiques exposed the persistence of “grey zone” regimes. Competing labels such as illiberal democracy and façade democracy culminated in Levitsky and Way’s concept of competitive authoritarianism, which reframes many ambiguous cases as diminished authoritarian rather than diminished democratic forms. The chapter then revisits the debate over structural preconditions versus political agency, contrasting modernization theory with elite-centered approaches, and highlights integrative perspectives that stress their interaction alongside transnational linkages. It advances a working definition of “successful democratization” based on five observable criteria, with particular emphasis on sustaining a reasonably level playing field across multiple electoral cycles. By adopting this threshold-based definition in place of the more elusive idea of democratic consolidation, the chapter provides a clearer standard for identifying when democratization has genuinely occurred and avoids conflating failed transitions with subsequent erosion. It closes by linking this definitional clarity to the study of democratic breakdown and contemporary backsliding, setting the stage for the analysis that follows.