This review discusses the anatase to rutile phase transformation in titanium dioxide (TiO₂), a key photocatalytic material. Anatase and rutile are two main polymorphs of TiO₂, with anatase being metastable and rutile stable. The transformation from anatase to rutile is influenced by factors such as temperature, time, and the presence of dopants. The review examines the synthesis, properties, and thermodynamics of anatase and rutile, and analyzes the effects of dopants on the transformation. A plot of cationic radius versus valence is presented, distinguishing between inhibitors and promoters of the transformation. The review also discusses the likely effects of various dopants on the transformation, based on their ionic radius and valence. The transformation is described as reconstructive, involving bond breaking and reforming, and is accompanied by a volume contraction of about 8%. The transformation is influenced by factors such as particle size, surface area, and the presence of impurities. The review also discusses the use of X-ray diffraction and laser Raman microspectroscopy to analyze the phase transformation. The effects of impurities and dopants on the transformation are analyzed, with a focus on cationic and anionic dopants. The review concludes that the transformation is influenced by the presence of oxygen vacancies and the valence of dopants, with certain dopants promoting or inhibiting the transformation. The review also discusses the importance of controlling the transformation for optimal photocatalytic performance.This review discusses the anatase to rutile phase transformation in titanium dioxide (TiO₂), a key photocatalytic material. Anatase and rutile are two main polymorphs of TiO₂, with anatase being metastable and rutile stable. The transformation from anatase to rutile is influenced by factors such as temperature, time, and the presence of dopants. The review examines the synthesis, properties, and thermodynamics of anatase and rutile, and analyzes the effects of dopants on the transformation. A plot of cationic radius versus valence is presented, distinguishing between inhibitors and promoters of the transformation. The review also discusses the likely effects of various dopants on the transformation, based on their ionic radius and valence. The transformation is described as reconstructive, involving bond breaking and reforming, and is accompanied by a volume contraction of about 8%. The transformation is influenced by factors such as particle size, surface area, and the presence of impurities. The review also discusses the use of X-ray diffraction and laser Raman microspectroscopy to analyze the phase transformation. The effects of impurities and dopants on the transformation are analyzed, with a focus on cationic and anionic dopants. The review concludes that the transformation is influenced by the presence of oxygen vacancies and the valence of dopants, with certain dopants promoting or inhibiting the transformation. The review also discusses the importance of controlling the transformation for optimal photocatalytic performance.