This paper explores the development of a transparent thin film speaker and its application in active sound transmission control systems for windows. The transparent thin film speaker consists of a piezoelectric poly(vinylidene fluoride) (PVDF) thin film coated with compliant transparent conductors. The developed thin film speaker shows good acoustic response over a broadband frequency range, and has the advantages of being flexible, transparent, and lightweight. Experimental results are presented showing that over 10 dB reduction in sound transmission can be achieved globally. The transparent thin film actuators can thus be effectively used as actuators for active sound transmission control systems for windows.