Chemiluminescence is a phenomenon in which an electronically excited fluorescent molecule is generated during the chemical reaction and emits light as a visual output. Although there have been numerous investigations of chemiluminescence so far, a lot of problems unsettled are remaining, for example, a question of what is the high-energy intermediates that interact with fluorophores. In this review, our investigations on chemiluminescence from the viewpoint of organic chemistry are described, emphasizing the mechanistic studies and the application of peroxyoxalate chemiluminescence. Employing various reactive oxalate derivatives, the kinetic studies allowed us to suggest the structures of the high-energy intermediates in the peroxyoxalate chemiluminescence. The chemiluminescence of the suitable phosphonate carbanions during the oxy-Wittig type reaction was also mentioned, in which the phospha-1,2-dioxetane is the most likely high-energy intermediate. Some chemiluminescence reactions were connected with ligand-metal ion host-guest chemistry to get a useful hint for further application of chemiluminescence to chemical detection.