During the past century, numerous cities around the world have introduced Grade Separation Pedestrian System (GSPS), including Underground Pedestrian System (UPS), skywalk systems or a combination of both, as an alternative way for pedestrian circulation to overcome the limitations of congested and traffic compromised street networks. This paper provides an overview of the development of GSPS across the world, and discusses the varied issues and debates relating to the development rationale and impacts of GSPS. The literature review indicates that GSPS were implemented in various cities due to various considerations and they have varied impacts on the city and its people both positively and negatively. As a relatively new topic in urban and transport studies, GSPS highlights important issues and questions that are deserving of more in-depth research. This research suggests that five research aspects need to be updated: new drivers beyond what has been presented in previous research; evidence-based research of GSPS in different cities; quantitative assessment of the development of GSPS; comparisons of the development patterns of such systems in the world; and the development of GSPS in developing countries.