Many applications, such as tone-signaling, audiosignal, hearing-aid feedback, or mains rejection systems, require bandstop (notch) filters to eliminate undesirable signals. One can achieve these signal reductions by using active bandstop analog filters. The bandstop filter circuit topologies considered in this article are Sallen-Key, multiple-feedback, and Bainter. Each circuit produces a second-order bandstop filter, with one pole and one zero in the transfer function.