Sushi is roughly classified into a group of 'Haya-zushi' (fresh sushi) using fresh seafood, and a group of 'Nare-zushi' (fermented sushi) which is seafood kept in rice and fermented by the action of lactic-acid bacillus.
大別すると、生鮮魚介を用いた「早鮨」系統のもの、魚介類に米を加えて乳酸発酵させた「なれ鮨」系統のものに区分される。