Luminescence is often weakened or quenched at high concentrations, a phenomenon widely known as ‘concentration quenching’. A main cause for the quenching process is mechanistically associated with the ‘formation of aggregates’, which is probably why the concentration quenching effect has frequently been referred to as ‘aggregation-caused quenching’ (ACQ). In 2001, we discovered an uncommon luminogen system, in which aggregation worked constructively, rather than destructively as in the conventional systems. We found that a series of silole derivatives were non-emissive in dilute solutions but became highly luminescent when their molecules were aggregated in concentrated solutions or cast into solid films. Since the light emission was induced by aggregate formation, we termed the process ‘aggregation-induced emission’ (AIE). Currently, the AIE luminogens have been applied in many fields, such as electronic devices, biosensors, chemosensors, and theranostics.