The article reviews the anatase to rutile phase transformation in titanium dioxide (TiO₂), a crucial photocatalytic material. TiO₂ exists in two polymorphs: anatase and rutile, each with distinct properties and photocatalytic performances. The transformation from anatase to rutile is irreversible and occurs at elevated temperatures, typically around 600-700°C. The review examines the synthesis and properties of both polymorphs, the thermodynamics of the phase transformation, and factors affecting its observation. It also discusses the effects of dopants on the transformation, presenting a comprehensive analysis of reported effects and mechanisms. The study identifies a boundary between inhibitors and promoters of the transformation based on cationic radius and valence, and predicts the effects of dopants for which experimental data are unavailable. The importance of doping methods in achieving equilibration is highlighted, emphasizing the need for careful control of synthesis conditions to optimize photocatalytic performance.The article reviews the anatase to rutile phase transformation in titanium dioxide (TiO₂), a crucial photocatalytic material. TiO₂ exists in two polymorphs: anatase and rutile, each with distinct properties and photocatalytic performances. The transformation from anatase to rutile is irreversible and occurs at elevated temperatures, typically around 600-700°C. The review examines the synthesis and properties of both polymorphs, the thermodynamics of the phase transformation, and factors affecting its observation. It also discusses the effects of dopants on the transformation, presenting a comprehensive analysis of reported effects and mechanisms. The study identifies a boundary between inhibitors and promoters of the transformation based on cationic radius and valence, and predicts the effects of dopants for which experimental data are unavailable. The importance of doping methods in achieving equilibration is highlighted, emphasizing the need for careful control of synthesis conditions to optimize photocatalytic performance.