A series of new linear and cyclic polyenes including siloles, butadienes, cyclcobutenes, fulvenes, and 4H-pyrans are designed and synthesized. When molecularly dissolved in common organic solvents, all the polyenes are practically nonemissive. Addition of poor solvents induces the polyenes to cluster into nanoaggregates, which turns the emission of the polyenes "on and boosts their luminescence efficiencies dramatically (hence "aggregation-induced emission or AIE). The emission color ranges from blue to red, depending on the chromophoric structures. Polyene nanoparticles on TLC plates show bright blue fluorescence which switches off reversibly in an atmosphere of volatile organic compounds. Addition of poor solvents to solution of cyclic polyenes bearing cholsteryl moieties leads to polarized green and anisotropic red emissions dependant on the solvent ratios. The different emissions may be caused by different packing patterns of the polyene crystals under different conditions.