Conjugated polymers recently have drawn much attention as an emerging sensory material due to their meritorious signal amplification, convenient optical detection, readily tunable properties, and easy fabrication. We review the molecular design principles of sensory conjugated polymer recognition events, which can trigger conformational change of the conjugated polymer, induce intermolecular aggregation, or change the distance between the conjugated polymer as an energy donor and the reporter dye molecule as an energy acceptor. These recognition/detection mechanisms result in mainly three types of measurable signal generation: turn on or turn off fluorescence, or change in either visible color or fluorescence emission color of the conjugated polymer. In this article, we highlight recent advances in fluorescent and colorimetric conjugated polymer-based biosensors.