Abstract: The worldwide energy revolution has accelerated the development of renewable-rich power systems, and numerous renewable energy technologies have penetrated as the main resources via power electronic interfaces. These new technologies exhibit control-dominated dynamic characteristics, which are largely different from synchronous generators. The high penetration of renewable energy technologies is altering the dynamic characteristics of power systems in a comprehensive and profound way. This paper overviews the transient synchronization issue brought by the connection of renewables to power systems, involving both the device level and system level. At the device level, the transient synchronization stability of renewable energy technologies is analyzed in terms of static instability and dynamic instability. The analysis methods, loss-of-synchronism mechanism, stabilization measures of two types of strategies, and grid-following and grid-forming synchronization controls, are summarized. At the system level, emerging interaction phenomena and instability mechanisms in different typologies of power systems with multiple generation devices are surveyed. Finally, the main conclusions of the existing studies are summarized, and the possible future directions for transient synchronous stability of new energy power systems are discussed with respect to the limitations in the stability classification, analysis methods, control methods, and stability studies at the system level.