In 1990 Krivine introduced the notion of storage operators. They are $\lambda$-terms which simulate call-by-value in the call-by-name strategy. Krivine has shown that there is a very simple type in the AF2 type system for storage operators using Gödel translation from classical to intuitionistic logic. Parigot and Krivine have shown that storage operators play an important tool in classical logic. In this paper, we present a synthesis of various results on this subject.