The need for chemical and biosensors that quickly and reliably detect clinically important biological molecules and toxic chemicals has been rapidly increasing. However, developing such reliable sensors and sensor arrays remain a significant challenge especially given the difficulty in devising an effective label-free and sensitive detection strategy. Conjugated polymers (CPs) have become emerging materials for many useful applications due to their readily tunable properties by variation of chemical structure. Particularly the sensor application of CPs has gained much interest recently because CP-based sensors can provide large signal amplification. Our self-signaling optical sensors are designed to achieve high sensitivity by means of the energy harvesting property and highly emissive property of conjugated polymers. Receptors are rationally designed to provide specificity toward a target analyte to realize high selectivity. We have developed conjugated polymer-based optical sensory systems to detect various target molecules such as DNA, proteins, metal ions, influenza virus, antibiotics, prostate specific antigen, nerve agents, and melanine. The concept, design principles, and applications of conjugated polymers for self-signaling sensors and sensor arrays will be discussed. Novel sensory systems based on emissive super-cooled liquids and metal-free purely organic phosphors will also be presented.