This special issue on police legitimacy assembles a group of articles that debate the core conceptual and measurement issues about police legitimacy by authors from different backgrounds. These issues are very important given the growing expansion of the literature around the concept of police legitimacy. We organize this issue to provide the platform for authors to express views and critiques around both conceptual and methodological issues of police legitimacy. Legitimacy is quite important for legal authorities, as people obey the law and cooperate only when they consider the legal authorities to be legitimate. The study of police legitimacy is largely directed by Tylor's work. Legitimacy is defined as "a psychological property of an authority, institution, or social arrangement that leads those connected to it to believe that it is appropriate, proper, and just" (Tyler 2006, p. 375). Following Tyler's approach, large number of previous studies regarded the obligation to obey the police as the measurement of police legitimacy, and they identified procedural justice, distributive justice, effectiveness, and lawfulness as the four major possible sources of police legitimacy. However, Tankebe (2013) initiated a new approach by arguing that procedural justice, distributive justice, effectiveness, and lawfulness were constituent components of police legitimacy but not potential sources. This round of debate was stimulated by a paper published in Issue 13 of the Asian Journal of Criminology titled "Police Legitimacy and Citizen Cooperation in China: Testing an Alternative Model" by Sun et al. (2018), in which the authors tested the new model for police legitimacy proposed by Tankebe (2013) instead of the most frequently tested framework-Tylor's process-based policing model. In that paper, by second-order confirmatory factor analysis and structural equation modeling analysis of a sample from a city in Southern China, Sun et al. supported Tankebe's work that police legitimacy actually comprised the four aspects: procedural justice, distributive justice, effectiveness, and lawfulness, which influenced people's obligation to obey the police and cooperate with the police. This result stimulated a wave of debate around the conceptual and measurement issues of police legitimacy. As the research of Sun et al. was conducted in China, a society with a totally different