Recent research and development of colorless and optically transparent polyimide (CPI) films have been reviewed. CPI films possess both of the merits of conventional aromatic PI films and common polymer optical film; thus have been widely investigated as components for microelectronic and optoelectronic fabrications. The current review coveres the latest research and development for CPI films, including synthesis chemistry, manufacturing process, and engineering applications. Especially, this review focuses on the applications of CPI films as flexible substrates for optoelectrical devices, such as flexible active matrix organic light emitting display devices (AMOLEDs), flexible printing circuit boards (FPCBs), and flexible solar cells.