Sound transmission through an unperforated partition may be described as the vibro-acoustic process in which fluid-borne sound waves incident upon the partition from the source side force it to vibrate and consequently radiate transmitted fluid-borne sound waves into the space on the opposite (receiving) side. Active reduction of sound transmission through partitions, or active sound transmission control (ASTC), denotes an active modification to this process. It may be defined as the reduction of transmitted sound through the action of electro-mechano-acoustical devices regulating any or all stages of the vibro-acoustic sound transmission process. In certain analyses, this branch of active noise control has referred to situations in which electro-mechanical actuation is applied only to a partition through which sound is transmitting. However, since ASTC may be achieved by other means, and since much research in the field has utilized other techniques, this limitation is clearly too restrictive. This paper reviews and categorizes many research efforts in the field, and provides a brief history of the efforts based on an extensive bibliography of the subject matter. It also identifies research areas that could be pursued in the future.